Getting back on topic, some other DC recommendations:
WSB 2K2 - avoid 2K1 as it doesn't have the Home Run Derby
Toy Commander - this is a really fun game, but can frustrate you as you go along. Some of the missions are very tough, and have no room for error. For the uniqueness alone this is worth a look.
Shenmue - either you'll love it or you'll hate it, but you won't know until you try
Power Stone - see above. It's a great fighter, IMO.
Seaman - you'd be hard pressed to find anything else like it. Comedy for the console.
Ecco - heard great things about the visuals, trying to secure a cheap copy myself
NBA on NBC - I liked this game from the arcade (playing in between classes), so I picked it up. There are other versions, but I've found nothing wrong with this one.
Hydro Thunder - Don't listen to those who tell you to pick it up on another console. I've played every single version (MAT3 included) and this is hands-down the best version. Only complaint I have about it is exiting to the menu after every race. Otherwise, arcade perfect (although I haven't heard the boat captain talk about 'millions of polygons,' but I just may not have been paying attention).
SF Rush 2049 - fun. Not much else I have to say. It's also on MAT3, but get the original.
Just because SEGA released something in a compliation or rereleased it on another console doesn't mean it's better, or it's even close to good (Sonic Mega Collection-GC comes to mind). IGN is re-reviewing all the DC games for sweet, sweet nostalgic goodness, so check that out.
http://dreamcast.ign.com/articles/702/702841p1.html
Also, there are several of us remaking covers so they fit with the other current gen games. Check out the classic forum.