Is plasma a constraint? You can get some fairly large LCDs and some pretty thin projection TV's.
It hardly makes any sense to get an SDTV nowadays. Standard def. broadcasts are going to cease in not too much time. Unless he's planning on replacing his set within < 3 years time, I'd get an HDTV. Also, a number of the smaller plasma sets aren't true HDTVs. They're called something like EDTVs, and they have a lower resolution than HDTVs. I wouldn't spend my money on any of those, either.
I look at
www.extremetech.com for a lot of my computer hardware buying decisions, and they have a section on HDTVs. They wrote out a buying guide with several recommended models
here.