Brands of hard drives are going to be a lot like stereo equipment... everyone has their favorite and has a horror story about another. I personally use Maxtor drives (what other people swear against) with zero problems. I have 16 Maxtor drives next to me spinning away... some for over 6 years... with zero problems.
I would recommend getting an external hard drive case that can hold two (or more) drives and setting up a RAID1 (mirror). What this will do is write all the information to both drives, such that if one fails... the data will still be safe on the other drive. This will work for 400GB or 500GB drives, but much larger than that (1TB for example) it is hard to find single drives that large at any decent price/GB. If you want larger than 1TB, then I'd say getting a RAID5 would be the best option... but things tend to get expensive quickly at that stage (unless you build it yourself).
As for size... I'd buy what you need now (and for maybe 1 year) and then buy more in the future. Hard drives are getting cheaper and cheaper and larger and larger. You can get twice and much space for half as much money this year compared to last, and the year before then (I built 4x120GB 6 years ago for the same price as a 4x250GB three years ago, as a 8x300GB last year).
How much space do you really need? I shoot professionally ~13 events (three-four days each) at about 16GB/day. So far this year I have 193GB... and last year shot 396GB. On my 2.2GB RAID5 I have photos going back to 2002 and still have ~800GB left. Getting 300GB or 400GB drives should be enough, unless you're shooting a TON of images every day/week.
-Todd...
