davidbarbarisi.com

I found a good article about how to keep youself safe while using public wireless Internet access (or WiFi). Here's some of the key points:

1. Don't use Internet Explorer - Use Firefox or some of the other more secure web browsers.
2. Don't visit web sites that require you to log in or enter sensitive information. It's very likely that your data is traveling in plain text and can easily be picked up by other WiFi users.
3. Only enter sensitive information on web sites that have https at the beginning of the URLs in the address bar. The "s" means your data is encrypted on those sites.
4. Gmail is currently the safest web based email, but you have to make sure to use the https version of the URL, https://mail.google.com/. But the article is a few months old, so most likely the other webmail services have implemented this too, but I haven't tried it. Last time I used Hotmail or Yahoo Mail they only encrypted login information, not actual messages. Gmail always encrypts login information, but I think it only encrypts messages when you request the https version of the site.
5. Using email from a program, such as Outlook, is a little trickier to do safely, but it's covered in the article. Most likely your email login information and messages are sent in plain text.
6. There are a few ways to do secure instant messenging. One way is to use Skype, but the other person must have Skype too. Another way is to use GAIM and an encryption plugin for GAIM. Both solutions are covered in the article.

The last two points involve installing programs and messing with settings, so at least stick with the first four, and just don't send any IMs with anything important. Although using Firefox means you have to install it, it's not so bad and it'll go a long way towards safer web browsing.

Here's the article. It includes a few more options and a lot more details.