The gaming system of choice among my students are the Nintendo DS/DSi and Wii.
I love my DSi (I'm really just a big kid). I used to have to travel a ton for work and the DSi is an awesome little handheld with crazy battery life. You can play new games, or Nintendo has released all of the classics for them as well.
Couple a purchase of the Nintendo DSi handheld with a purchase of the
R4i flash card and you can have every DS game ever made for Nintendo on one game cartridge for under $30. If you have kids and you don't feel like having to talk to them for the next couple years I'd suggest this option.
Additionally Nintendo has announced that their next-gen handheld will be the DS 3D. It will be a 3D technology that won't require users to wear glasses and according to the article from the NYT it will be available within the next 12 months. If Nintendo pulls this off they will continue to dominate the handheld market for the foreseeable future: http://www.nytimes.com/2010/03/24/technology/24nintendo.html