Surly "Nice Racks" are made from chromoly-steel tubing - sturdy hardcore stuff. I want to get one for my 520 - well that or another steel type. Aluminum racks are cheaper, but aren't as durable. I've broken an aluminum rack (rated for 50 lbs.) with only 20 lbs. on it (I suspect it was a factory defect). Steel racks are more expensive but more durable in the long run. Cost vs. Quality - in my opinion ( & experience) - I'd go quality everytime.
Also, Panniers are handy as hell. I've got a great (and cheap) pair of Banjo Brothers Saddlebag Panniers. Great for around town, commuting, hauling grocieries, etc. If you plan to do touring I'd purchase some higher quality ones - but the Banjos have suited me fine for general use. Ortliebs are on my short list of new touring panniers. I'm sort of taken by some retro-grouch waxed cloth Ostrich brand panniers but I'm sure I'll reign in that desire and go practical.
"Things look different from the seat of a bike carrying a sleeping bag with a cold beer tucked inside." ~Jim Malusa
2009 Trek 520-Brooks B-17 Special in Antique Brown
2010 Surly Long Haul Trucker-Brooks B-17 Standard in Black
1983 Fuji Espree Single Speed-Brooks B17 British Racing Green