While not new, my friends and I are really enjoying Tetris DS for the Nintendo DS.
One impressive thing about this game is that there is a vs. mode allowing up to TEN people to play with only one cartridge! So a group of my friends are planning, in the near future to get together and play vs mode together (since all most of us need is our DS present)
I’ve noticed a lot of great DS games have this feature (well, I know it goes back to Gameboy advance). I got Elite Beat Agents and discovered that the download mode for that game also supports up to 4 players.
Probably my favorite thing about this is that unlike the old-school gameboy, everybody doesn’t have to have the same game (although if you do, it often allows for even better multiplayer modes). So if each of us has a single, different game with download multiplayer, when we get together we have essentially 4 different multiplayer games to play