If you are using one and the same address more then once in order to send or receive your E-mail, you are "creating" an identity with it. In the following you will find notes about web mail services as well as some web services designed to improve your privacy:
If you want to send E-mails, but do not want to reveal your identity to the addressee or a third party, the best thing is using an anon remailer. Some mixmaster remailer offer a web interface. If the addressee has a contact form on his web-site, of course, you may use rather that one.
If you are registering on web-forums you often have to leave an E-mail address in order to get a confirmation. If you do not want to use your own E-mail address for it, you may use rather one of the following temporary PO boxes. You can use addresses from this PO boxes without any registration.
Two websites for temporary e-mail accounts. The accounts are limited to a short time and automatically deleted afterwards.
Pseudonymous inboxes for whistle-blowers
Journalists, bloggers and other whistle-blowers may use the PrivacyBox.
E-mail accounts in one minute
There are many E-mail provider that allow you to set up a new account very quickly if required. Choose an E-mail address of the form anonymous1234abcd@provider.tld, that is "anonymous" + numbers + letters. If all JonDo users create addresses of this form, they are much less distinguishable. Please be aware that you do never access these accounts without using JonDo because otherwise your IP address is being revealed. Please note that almost all of these services need cookies for login.
The JonDo help contains a short tutorial for using Mozilla Thunderbird with JonDonym.
With Hushmail you can prevent the details of your E-mail communication being left behind on servers and/or computers of your communication partners. Above all this is useful if the addressees of your E-mails are using web accounts which are never deleted, like GoogleMail. At least the E-mail provider can trace your communication then. Therefore, act as follows:
If your conversation partner is also using Hushmail, however, he keeps your messages. You should encrypt your messages using GPG additionally, (best directly in your web browser) in order to make the access of a third party more difficult.
If you want to send larger documents, you may not be able or not want to attach them on E-mails for various reasons like risk of attachment truncation or loss, or even rejection of the complete mail (receiver won't even notice that you tried to contact him), caused by various attachment size or type limits or even complete ban of them on the way, by the receiver or his provider. Then you can use a file hosting or sharing service, preferably one with a time limit or possibility of deletion by the uploader. List of services (without pointing privacy issues): TheFreeCountry.
If you want to protect the contents of the uploaded files against being accessed by file hosts or third parties you should encrypt them before uploading. You may use, e.g. TrueCrypt, AxCrypt, AES Crypt, 7-ZIP (the own 7z format is very secure) or jFileCrypt. Then you send the password to the same people that get the download link to the files.
Hint 1: An asymmetric encryption of these files using GPG/PGP results in third parties being able to connect your GPG/PGP pseudonyms with those files.
Hint 2: A banal ZIP file with a password set is a bad idea since the "standard compatible" ZIP has a very poor "encryption", while the "advanced" ZIP files have better algorithms but are very incompatible.
Long term file hosting
Short term file hosting and sharing
Image hosting
Text hosting / pasta
Instead of installing software on your PC, you can submit the job to an online converter. Of course this is bad for your privacy, even more considering that most of such converters require JS or even registration + payment.
Document conversion
Software for local document conversion exists may bring problems like very large size, high requirements, painful installation or payment requirement, so you could give a chance to an online converter, for non-private documents at least.
Image and video conversion
Many online services exist, but better use some of good and free software products for local conversion: XNwiev or NConvert for images, FFMpeg or FFMpeg2Theora for videos.
There are 2 ways to provide online video: Flash + JS and HTML 5 Theora. Obviously the latter is much better for your privacy, but most pages stick to Flash. In some cases it can be possible (was more common in the past, still applies to "blip.tv", see below) to "pick" the video manually from page source, but the common deal is "No Flash, No video". For HTML 5 Theora handling JS is used by Firefox browser and Wikimedia Commons page, but also without JS videos are still accessible for playing (possibly outside of context in a separate page and without progress/time info) and download. Note that online video performace will be unsuably bad with any free anonymization service, and the download will take at least 10 times longer than the playing time (wait at least 1/2 hours for 3 minutes clip). So storing the video link and downloading the video later without any anonymization is worth considering. Forum thread: 4477 (English). More information about Flash video downloading with JondoFox see Download web videos and jondofox2.html#videoDownload.
The forum market is covered by several major competitors (phpBB2, phpBB3, v-bulletin, ...) and many "special" forums. JS is usually not required for forum usage including posting, it is just used for marginal things like smiley and BBcode inclusion, but in some forums it may be required for registration (as abuse prevention), or viewing user profiles or searching. Forum permissions, like the ability of guests to post or view profiles, are highly cofigurable by the administrators in all major forum solutions, nevertheless there exist also modified versions of such forums, exposing non-standard behavior like additional security precautions, possibly including JS requirement or referrer checks. Almost all forums do store IP addresses of all posts and give the moderators and administrators permissions and tools to view and evaluate them. Registration is required to post almost everywhere, guest posting, being the standard years ago, got disabled after excessive abuse (trolling, flamewars, automatic spam posts, sockpuppertry) encountered over the time.
Most Wiki-like services work without JS, just advanced features like special character inclusion are not available then. Cookies are required to login.
Many cheap and free webhosts don't offer FTP, instead they provide a HTTP web based system for upload and management, usually requiring not only Cookies, but also JS.
Make sure to have Cookies and Javascript disabled when using search services. At first try privacy friendly search engines like Ixquick (SSL-secured) or Cuil.
At most all map services need Javascript for searching places or streets.
Street View (Google) or Street Side (Bing, Microsoft) are not secure useable with JonDonym. Flash or Silverlight are needed for displaying. Both plugins are disabled in JonDoFox for security reasons.
Many such pages do require JS enabled, otherwise they complain or simply fail. Online ticket purchase or reservation is bad for your privacy.
Cookies required to login, may require JS also. You are not anonymous to your bank anyway, the bank knows both your name and your home location, and the communication contents is protected from your provider and 3rd party by HTTPS, so it may be a good idea not to use any anonymization service at all. If you use it nevertheless, you can just hide your login location from the bank and the name of your bank from the provider. Enable Cookies (and JS if required) before login and disable them after, on both occasions also clear all private data of the browser. Don't access other pages or use other software accessing the Internet while logged in. Avoid browsers with limited or no HTTPS support. About JS requirement you can complain to your bank, security is the "killer argument" here.
Bad, browser Java plugin needed.
Needs Flash + JS or Java plugin or installation of special software, no way to do with pure HTML, very bad for privacy. Only good way is special software respecting proxy settings, it can than be used with paid JAP services only.
Will usually pressure you to enable JS or Flash or to install or "update" something, or to call an expensive phone number, high risk of privacy intrusion or virus capture. Easy solution: avoid such pages completely.