Many of the major game publishers regularly host focus groups where gamers are allowed to play an upcoming game and give feedback. I live in the Dallas/Fort Worth area and I've participated in focus groups for both Gearbox (the Borderlands people), and Bethesda/id (The Doom/Quake/Wolfenstein people).
It's rewarding to tell the group moderator "Yeah, that part kinda sucked." and then when the game comes out you see that they changed it or removed it. And you always get some neat swag for your time as well. I did a focus group with id on Thursday and they gave me a nice T-shirt and a Fallout bobblehead.
The focus groups I've participated in require you to be at least 18 years of age, and there are non-disclosure agreements and other legal forms that you have to sign before you can participate You also have to be able to provide your own transportation to wherever the event is being held.
Here's a link to the Bethesda signup page. I'm posting this because they specifically said that they need more testers.