The market for high-end AGP video cards will exist at least through 2005. After that, expect the market to slowly phase out AGP in the high-end (and eventually middle-end) segments much like the phase-out of PCI video cards.
If you want a good 939 board under $150, I'd go with either the EpoX 9NDA3+ or the MSI K8N Neo2 Platinum. Both got great reviews on Anandtech, and both are great overclocking motherboards.
I would go with the EpoX, just people there seems to be so much polarity about how good the MSI board is; the EpoX seems to get favorable user reviews from most people. However, there are much fewer reviews overall for the EpoX, so that may be the reason (the MSI is quite popular; lots of reviews to peruse on Newegg and in forums).
Gigabyte also makes a 939 NF3 Ultra motherboard, but it goes for $200...ouch.
Some people like 939 boards based on VIA's K8T800PRO chipset, but in pro reviews they are consistently outclocked in their max FSB by NF3 based boards.