Friends- Got a free Dreamcast with three controllers, 2 VMU's, and Gauntlet Legends from my sister-in-law!
Flea Markets- Not so much anymore b/c there is only one near me, and it usually has nothing new to offer.
Ebay- So addicting.
Gamestop- For GameCube games.
The Digital Press Store- Went there for the first time last week. About a two hour drive, but tons of good stuff!