For me, when I'm getting a new or 2nd-hand GFX card, I will take a look at the list below and compare the card with others with similar price tags. I will take it if it's ranked considerably higher among the cards at its price range.
http://www.overclock.net/graphics-cards-general/270292-graphics-card-ranking-3rd-time-s.htmlBy the way, the list mixes AGP and PCI-E cards. AGP cards are getting obsolete and expensive, thus go for PCI-E ones, and take note of that when choosing a card from the list. Otherwise, you may head down to SLS asking for a AGP 8800GT and the ah bengs there will be laughing damn hard at you. Ask the sa jiao queen to go with you to get more discount as well.
For the choice of motherboard, if you're overclocking, go for Asus or Gigabyte. Google for online reviews about them if you're really into OC. Otherwise, just take up any board that is able to support your processor and has the features you want, such as a FireWire port, eSATA support, integrated WiFi etc.