Personally, I'd say use Jpegs and balance the compression with final size so you get something that compromises both good looks and file size. I've done some examples below to illustrate my point. All are Jpegs with 80% quality and the file sizes are much more friendly to the forums than the PNG files you folks are using. Hope this helps and that you could use them to help speed up forum browsing.
http://img170.imageshack.us/img170/3...3jpg20kte4.jpg
http://img170.imageshack.us/img170/3...tesigjpxx9.jpg
http://img80.imageshack.us/img80/716...4jpg24kpb1.jpg