You'll want Silent Hill 2 if you like horror games, although I think that's what you meant by Silent Hill. Get Devil May Cry and Devil May Cry 3 as well, try to get the special edition pack as well (extra features, it was released after the original Devil May Cry 3). Rune: Viking Warlord is definitely a hidden and unknown gem. Imagine a Viking game which lasts a long time and was, well, done right. The fighting is nothing short of fun as hell.
Hitman 2, Contracts and Blood Money are also very fun games. Although I preferred Blood Money quite a bit over 2 and Contracts. However, if you already have Hitman on the PC, Contracts is really just a console version of that. Prince Of Persia is also a good game to check out and it's sequel, Warrior Within, is a very debatable game if it's good or not. I liked it but some don't. That's really when the series died.
I'm going to guess you have Grand Theft Auto: San Andreas and the rest of the Grand Theft Auto series down, as well as Time Splitters. I think the only other games I can think of right now is Stuntman if you're into driving, Freedom Fighters if you want to take a lucky dive (very hit or miss), the Jak series up to 3 and the Soul Calibre series if you're into fighting games.
I may think of more after I get back from school, so I'll probably edit my post much later.