Looking for good games for under $20

Hi everybody...

I am a brand new to the pc gaming universe and am hoping to get some new games that really pack a punch for under $20 on steam. if you could tell me and other people on the forum about some good games it will be greatly apreciated.

thanks!!!

Steam:

http://store.steampowered.com/search/?price=0,10#category1=998&price=0%2C20&advanced=0&sort_order=ASC&page=1

Good ol' Games:

http://www.gog.com/catalogue

It all depends on your definition of pack a punch. Some people love Call of Duty, others think Hello Kitty Island Adventure is top knotch.Those two sites should get you started, just narrow it down by the genres you like and enjoy.

www.indiegala.com

Here's steams advance search, under $20, sorted by metascore.

My personal recommendations from that list would be Half-Life 2, Bioshock, Quake, Deus Ex, to get some of your PC FPS history covered. Also available on the cheap is my #1 favorite game of all time The Longest Journey, although it's a pretty hardcore adventure game and may not appeal to everyone. 

Counter Strike: Global Offensive is pretty good. I bought it some days ago and I'm really happy with it. Portal 1 and 2 are a must, IMO. Left 4 Dead 2 and Killing Floor are pretty good and around that spot (Killing Floor costs a bit more if you buy the extra content).
As for simpler sprite-based games that are a lot of fun. Lately I've been playing a lot of Awesomenauts. Castle Crashers is also lots of fun. Those are the ones off the top of my mind.