Agree with Matt, I have used Macsales.com and enjoyed they're drives. I picked up a Mercury Legacy Drive (PATA) for my powerbook and it has been a great drive. Just ordered a sata one for my 3000D.
For $100 or so you get an extremely fast and quite drive, admittedly no old system will be able to leverage all the speed that a SSD can deliver, but SSD's are so nice. I'm not going back to spinning drives again!!!