Ok off the top of my head, here is my top 5:

Reorganise the data on this site - sitemap, structure, cross link knowledge thats tucked away (to keep this under 5 points I am also going to add tutorials on the latest technologies in to this point)

New site design - doesnt add any value to the sites function but it would make a big difference to the enjoyment I get out of using the forums

Auto link in firefox - I spend hours making hyperlinks in firefox - I bet I have already spent over a day of my life.

Inbox highlight - Its a hassle to check my inbox, make it really clear to me when I have a new message / reply waiting for my attention

Better thread tracking - Let me see when I got a question right for somebody (discern it from the threads I participated in but didnt hit the mark), let me see clearly when the thread author has replied on a thread (which means new facts for the problem have probably come to light, rather than just opinion on the problem)

And to put them in order?

1 - Auto link
2 - Better thread tracking
3 - New site design
4 - Inbox highlight
5 - Reorganise the data


Pretty much everything else on my list is really just "nice to have"s.