If you're looking for a small portable drive, Simpletech wouldn't be my first choice. They use a larger hard drive and requires an external power source. The WD 2.5 drives are driven by the USB 2.0 Bus which make them perfect for portability, and no powerbrick to lose. The Seagate is also very speedy and great for Video. The WD 2.5" drives are slow, and wouldn't be a good choice for Video, but great for backup, or use as an external for standard files, and Itunes. I have 90 GB of tunes on mine.
If you're looking for a desktop and speed, the Seagate Pros are a great deal, often on sale, have Firewire, USB 2. and Esata connections. The powerbricks are also small and light, and one piece rather than the standard two piece. They are also in a vertical case so they take up very little space. I bought a 750 GB new on sale from Amazon for for $199 on special. Later, a second drive at Costco, $215 with a $10 rebate. The Seagates also have no fans using the brushed aluminum case for a heatsink. A very quiet drive that will also power itself down when not in use.