A lot of this is down to personal choice, but some important features:
1) Lcd for sure, Plasma bulbs don't last long, and cost £££ to replace
2) HDMI x 2 (even if you don't need them yet)
3) DVI input for your PC
4) Built in freeview (minimum) and built in freesat if budget allows.
Your choice of Panasonic is a good one. I have a 32" Hitachi in the bedroom, and a 42" Panasonic (older model) in the living room
One thing though...I found that the 42" is too big for the room.(if you have a very large living room you should be fine0
A few ideas!