http://pbwiki.com
In my opinion, this is probably one of the most useful sites for group work - a wiki. I'm quite certain nearly everyone has heard of wikis (think Wikipedia). As to if you've used one extensively (editing, participating etc) is another question, and I strongly suggest you give it a go. The nice thing about pbwiki is how easy it is to setup and use. The wiki markup syntax for pbwiki is probably one of the most user friendly I've come across, but it doesn't really matter since they also have a GUI editor (basically a WYSIWYG - What You See Is What You Get editor).

So what makes pbwiki so good for group work?
Short answer: It's a wiki
Longer answer: It allows everyone in your group to contribute to the discussion and throw in ideas. Everything is in one place, everyone can see the most updated information, and everyone can access everything. If someone accidentally deletes something, or you decide that an idea form a week ago was actually good but was deleted - don't fear - just have a look into the wiki history

http://assembla.com
This is a MUST if you are doing any coding assignment - Assembla provides you with Subeversion (SVN). It also provides a wiki, Trac and a whole host of other features, but the one I've found most useful is SVN. I won't go into the details, but the SVN repository will pretty much let everyone in the group work on the code at the same time and keep a running history of all the versions of your code (so if you accidentally do something horrible, you can revert back to the most recent working version). If you want to read more about the wonders of SVN have a look at Subversion's web page. Assembla also comes with a wiki, but I find pbwiki more user friendly.

http://drop.io
This is one of my more recent finds and haven't used it much but I do believe it will be very useful for file sharing. It basically lets you create a 'drop' - a place where you can store files online (up to 100mb). The distinguishing feature for drop.io compared to other file sharing sites is that it allows you to password protect your files. With the password, you provide users with different levels of access (View/View and Add/View, Add and Delete). In addition there is also an admin password which lets you change settings of your 'drop'. Another bonus is that to create a 'drop' you don't need to use your email address - just the name of the drop and a password if you want. The only drawback is 'drops' are only valid for at most 1 year, but it's not so much of a worry as you can always renew it.

So those are the three sites I If I haven't convinced you to at least try out one of the sites, I'll just mention now that they are all free If you have any good sites for group work that you know of, please share - I'd love to see what else is out there.

In my procrastination, I had google reader open and saw this...

A free DIY Linux penguin from fractalspin! Haven't yet printed and tried making it yet - but must find some time to do so! I see a lot of numbered tabs, but wonder how it all goes together? For the more skilled/talented people you can try and sew your own soft-toy version (see instructions at free-penguin.org). If anyone does try, tell me how it goes!