Hmm... There are quite a few for me! I'll go per console.
PC - ArmA: Armed Assault - Probably the first game I was properly into and the second title from Bohemia Interactive after Operation Flashpoint, I spent many days in the editor just putting together random missions and just messing around! I remember two 'missions' I did very well. The first was on the Sahrani Airport, spawn in hundreds of BLUFOR, OPFOR and Civilians on the runway, then just watch the massive firefight take place with plenty of explosions from just about every corner! (Two aircraft for both teams also shooting at everything in sight. I dunno, I was 8!
) The other is where you have to assassinate the Bus Driver, load up the squad into the bus, drive to the military base, board the helicopter and take over the airport. Definitely a lot of fun on that game!
Xbox (Original) - Pro Evolution Soccer 5 - Okay, so not exactly 10 years, but probably the BEST football game ever! Graphics at the time were amazing, gameplay was quick and full of action, I definitely enjoyed many hours of playing different leagues and teams. PES may not have always had the licensing, but at this time the gameplay was always on top and it dominated football games until around 2008. I've also got to give a shout to Project Gotham Racing which was also a fantastic game for the Xbox. Didn't complete it, not even close, but still many hours of fun and racing my brother.
Nintendo DS - Drawn to Life - This game is probably my number one game of all time! Drawn to Life had amazing characters, a fantastic story line and the hero was designed by you! I finished both the original and the not-as-good but still awesome sequel and loved every single moment I played those game! Whilst the game may not have been the most popular, I personally found no wrong with it and would probably return for the story of it again today!