I just assume everyone knows about the trial garden, but I've noticed a few newcomers lately, so here is a link to the 2004 results from UGA's trial gardens. This link is to the perennial trials. They also have separate trials for annuals. My favotie part of the results is that they tell the first bloom date for most of the plants and the number of days in bloom. Useful information when I'm trying to figure out what will bloom in a certain period.

Here is a link that might be useful: 2004 Perennial Trials