Apple doesn't make their own hard drives, they just charge more than double the retail price from their storefront.
You can pick up any SATA drive (the same drives that they sell on the apple store) from macsales, newegg, amazon or wherever and it'll work perfectly.
As for brands, Seagate, Western Digital, and Hitachi are the most popular, and what you'll typically find installed when you purchase a Mac Pro. As to what brand is more reliable, the evidence is primarily anecdotal. Different people have different experiences with both. I have both a Seagate Barracuda and a Western Digital Caviar and will probably get another 750GB or 1TB WD drive soon.