Okay, let's try this again, since the first attempt I could not quite get my wiki link to stick…
Most useful or fun? I'll say it again - the Big Huge Labs was a great tool to play with. That tops my list. I also use photobucket to share photos with relatives and friends far away, though I don't go the flickr route because I like the privacy settings. I am just not willing to put things out there for the whole world to see. I use bloglines and blogger all the time, so those are useful to me, but not new. What might turn out to be useful in the next while is del.icio.us - I am moving branches, and I think I might move my bookmarks on there for portability, since there are lots of sites I like to use for programme prep and kids ref.
And as to the wikis - here is one I find amusing:
