Check MMOHut if you want to see reviews & gameplay videos of F2P games
But, here is some games that are pretty good , P2P/F2P.
-Counter-Strike 1.6 & Source.
-World Of Warcraft , Private servers / Retail.
-Warhammer 40K Dawn of War 2,Retribution & Chaos rising.
-Grand Theft Auto : San Andreas
-Need For Speed : Most Wanted
-Left 4 Dead & Left 4 Dead 2
-Team Fortress 2 (F2P now, with limits)
-Call Of Duty 4
-Killing Floor (THIS GAME IS SO UNDERRATED)
- Super Meat Boy
I was too lazy to read every page so some of these maybe have been suggested already but you really should check MMOHut