In regards to external drives..... I'm an expert (unfortunately).
In my home I have over 6 Terabytes of storage, simply because it's been cheaper to buy more drives than take the time and effort to dump to DVD. Most of the 6TB is on external disks, and the majority of those drives now are Seagate External 300GB (in the well vented silver case).
I've used every major drive manufacturer... Maxtor is by far the WORST for external drives. I lost 5 drives within 2 months last year... oddly, right after their 1 year warranty expired! Western Digitals are reliable, Lacies tend to be pretty, but run VERY hot, and thus are prone to dying faster.... I've known more and more people that have experience this in the last 2 yrs.
While it may seem attractive to run externals on USB2, spend a little more and spring for Firewire. USB2 has a problem with I/O collisions, and thus can't sustain high speed/large file transfers nearly as well as Firewire.
One major suggestion, if you're going to use external drives... MAKE SURE YOU HAVE A BACKUP of everything you'd care to lose. Externals run hot, and usually dont have fans, tend to get bumped, and tend to have their power supply and/or controller go bad (in the last two situations you can put the drive in another case).
Hope that helps. Go for the Seagates.... of course use Froogle to find the best prices.
http://www.buy.com/retail/searchresults.asp?querytype=home&qu=seagate+firewire&qxt=home&dclksa=1