The N64 Zelda games. People say the graphics look dated, but I disagree. They have aged a bit but I think they still look good. They still do a great job of creating the aesthetic they are trying to produce. The gameplay of both games, especially Majora's Mask, still feel as fresh as ever.
Wind Waker! The cel shaded graphics haven't aged a day. It's the best example of cel shaded graphics that's ever been created, and I think it still does a lot better than the most recent cel shaded games (Borderlands, Crackdown, etc.). The gameplay is still fantastic too, just like the N64 games.
SSX3. The gameplay and controls still feel as tight and well put together as ever. It feels just like a game that could have been released just yesterday. Also the graphics still look good. Probably because they are very colourful and there isn't a need for tons of detail. It's mostly snow and neons.
Need for Speed Underground 2. Still got some of the best controls of any NFS game in the past decade, a great city to drive around in and a brilliant soundtrack. Some of the newer NFS games may have had better graphics and extra features but none (apart from maybe MW) have been able to bring everything together in such a perfect opus of everything that NFS did right.
Pokemon Gold/Silver/Crystal. As the series has gotten tired by repeating itself over and over the Gameboy Color games still stand up as among some of, if not the best games out of the whole franchise. It was the only time in the series when everything they added was good, nothing added was bad and nothing was taken out. The first generation games have dated graphics and they are obtuse and slow paces compared to later games, but the second generation games still have good pacing and the graphics and music are still great.