Walmart.com: Seagate FreeAgent GO 320GB 5400RPM Portable Hard Drive, Blue Morpho - Exclusive Walmart Color: Computers
I got this one from Wal-Mart for about 60$, has worked fine (cIOSX rev 17, Hermes 222 & 223, USB LoaderGX) even for the games that don't work for a lot of people (MH3, NSMB, GH:WoR), all purchased legally, of course.
Here is a list of known working hard drives. (This is an off-site link, meaning that it takes you away from www.wiihacks.com, thus, the information may not be supported on this forum).
USB Devices Compatibility List - WikiTemp
Nope, one partition, formatted as WBFS.