A few games that come to mind...
'The Mark of Kri' for PS2. It's a third person action/adventure game with a fairly unique fighting system (almost along the lines of a rhythm game), a bird you can control to scope out far away areas, and a great animated look a la Mulan and the like.
$2.75 used on Amazon
'24: The Game' for PS2. I've never seen the show, but the game is pretty solid for a budget price. It's been criticised for doing TOO MUCH. You've got driving levels, puzzle minigames, 3rd person action levels, stealth (if you choose), just a ton of content. And its got a very cool comic-book-ish design. The aiming and controls are different, but they work great. The camera kinda sucks and no one part of the game is outstanding, but overall its a lot of fun.
$7.20 used on Amazon.
'Downhill Domination' for the PS2. Made by the same company that put out 'War of the Monsters' (which Wombat mentioned), Downhill Domination was one of the great overlooked PS2 titles. It was pretty pricey in the after market for some time, I finally bit at $25 used, but has since gone down in price consiterabley. It's a downhill mountain biking game, you race to the finish line going off massive cliffs, through narrow gorges, and over all kinds of great terrain. There's forest fires to shoot through and lots of powerups to grab. It's a bit like Road Rash in that you can do battle with your opponents, but the main focus is hauling ass to the finish line. The levels are pretty long for a racing game too, with most taking over 5 minutes to complete. A lot of fun for just
$8.40 used on Amazon.