Matt, I hate to be a stickler, but a "good psu" may not be good enough for the newer video cards.
You have to check the manufacturers web site for the exact specs, but most new cards have VERY HIGH psu requirements to guarantee the video card runs properly and does not overheat due to drawing more amps than the "good" psu can deliver. For instance, many ATI and Nvidia new cards state they REQUIRE around 30 amps on the 12V rail. Typically that means at least a 450 Watt psu, but can mean up to a 750 Watt psu depending on the brand, etc... To make it worse, many high watt psu's DO NOT have enough amps on the 12V rail for the new cards.
So, unless you actually know for sure the 12V rail amps of your current psu you may actually have a "bad" psu - well bad for these new cards. Hopefully not, but better to be safe now than sorry later.