Some ideas I had for the bitcoin client:
It would be nice to click on the connections (in bottom right corner) and see who is connected to you. (IP addresses)
It would be nice if the Help had a help file, that explained what "verify message" does etc. The help isn't really a help screen at all!
Finally it would be nice to have an optional ticker that showed currency conversion next to BTC amount. I know that is not the point of BTC (comparing it to other currency) but an optional feature like this would be neat.
If I could program I would help!