If you want a good socket 939 MoBo, you will have to go with PCI-Express. Sorry, but the PCI-E boards outperform the AGP boards. IF you can tolerate that they're PCI-E, here are the best from ASUS and ABit.
ASUS: A8N-SLI deluxe
ABit: Fatal1ty AN8
If you dont like these, here is how to find more info on MoBos.
1)google.com
2)search for 939 motherboards
3)work out which boards interest you
4)goto the manufacturers website
5)if you still like it, google it for reviews. also look at anandtech.com and hardocp.com for reviews.
6)once you know which boards you are interested in, post here asking for peoples opinions on specific boards.
7)decided on a board
8)buy the board.
RoD