Advance Wars. Think of it as cute, Japanese Warcraft. (Not WoW, just Warcraft).

New Super Mario Brothers is super fun to play against one another - there are quite a few mini games, and there's a mode where one of you is Luigi and one of you is Mario and you run around getting all the stars and stealing them from one another.

I keep thinking I'll get bored of playing it, but so far everytime one of my friends comes over with a DS this is what we end up doing.

There's a single player mode that's fun too - your standard Mario sidescroller.

DS Tetris has lots of good multiplayer options, and, if you haven't played Tetris in years, lots of new versions. Clubhouse Games is a compilation of games like checkers, euchre and Othello--I'm a big fan, among other reasons because it doesn't involve insane video gaming skills. Ooh, and Animal Crossing might be a very good choice for a couple.

And, yeah, Mario Kart. Ooh, and I nearly forgot to mention--if you like Mario 64, there's a pretty good port of it for the DS.

More suggestions later as I think of 'em.

We both liked Pokemon.

I know next to nothing about it, but I thought I heard Nintendogs is kinda Pokemonesque.

(Or maybe that's tamagochiesque I'm thinking after looking at the website.)

Seconding Advance Wars, though it might be out of print. Age of Empires is also a good strategy game, much different from the PC version.

Also: Phoenix Wright Ace Attorney and the sequel. And Trauma Center: Under the Knife if you have a steady hand.

I'm really digging Age of Empires.

If you like platformers, Princess Peach was a good one that sort of got overlooked.

Otis: Cool. I'm up to level 8 of new Super Mario Bros, and was wodering where to go for a good platformer.

Hotel Dusk: Room 215 is the first game to make me want a DS.

Meteos - fun puzzle game

Advance Wars - Dual Strike (somewhat hard to find but you get get it used online if nothing else)

Castlevania - Dawn of Sorrow (really fun platformer)

Castlevania - Portrait of Ruin (if you like the above game, I think DoS is the superior game between the two)

Metroid Prime Pinball is fun if you like pinball games

If you did not have a Gameboy Advance, there are a LOT of games for it that are great fun and you can play them on the DS too.

So true. Super Puzzle Fighter is a classic block-dropping GBA game, and, my favorite series ever, Bomberman, is available across both platforms. If you're going to get just one, make it DS Bomberman Land Touch.

I slightly prefer Big Brain Academy to Brain Age--the tasks are more like puzzles, rather than strictly reading and math, and it doesn't emphasize daily performance (if I wanted to play a game that emphasizes daily performance, it'd be Animal Crossing).

I'd have to second the New Super Mario Brothers.

And, damn, Phoenix Wright is so much more fun and addictive than I'd thought it would be. It's superly awesome.