Not your mother's hard drive
For digital pack rats who have to save every little photo, there's the Apollo Expert UX external hard drive from Imation. Coming in at a svelte 2.5 inches and featuring a protective casing with a handy little stand, this will save your laptop's memory from screaming mercy. Price: $109.99 -James Park
Availability: Find out how long it takes to restore data if it's lost and whether there are different levels of availability for different types of data. You'll want to know exactly how long it will take to get your most critical data back online in the event of a failure.
Service-level agreements: How quickly do different vendors process requests for restoration, and what guarantees are there for response times? Get it in writing.
Financial liability: Know what's at stake. Find out what the financial implications are for loss of data if the backup service doesn't work or if backed-up files become corrupted. The safest bet is to have a backup for your backup, which is more feasible as service prices drop. --J.M.