Blu-Rays will play standard DVDs and upscale. Do some searching on the upscaling as some do it better than others. I haven't made the jump to Blu-Ray yet, but in "regular" DVD players, the upscaling chip used makes all the difference (not the the average user).
I bought my Hitachi plasma about 4 years ago and love it. However, I went with Hitachi over Panisonic because standard def looked better on the Hitachi than the Panny. of couse std def won't be an issue for much longer... I think the panel was made by Panny. Also, keep in mind when you're viewing stuff in the store, they're usually jacking the brightness and contrast through the roof. This is to "catch your eye" and to compensate for being under a hundred floresent lights. I usually check out
http://www.avsforum.com/ for candid reviews on whichever model(s) I'm looking at. It's geared for the techie weenie, so if you're just an "average" user, you may not find it more frustrating than helpful.