I've tried most major brands and some niche ones (both corporately and also for personal use) and each seem to have their issues, it very much depends on the brand line.....because not all laptops are created equal. Some lines are made specifically for business travels....they tend to be solidly built and have lower fail rates....BUT they come at a premium (IBM/Levano ThinkPad x60s). Others are more mass marketed and cut corners to keep cost down. That being said...just because it is expensive, doesn't mean it is rugged; the VAIO comes to mind. Great laptop (looks, performance, etc)......but they can be fragile.
I have a Dell 700m (inspiron) and it has been great....but i've had little things go wrong with it, mostly because of the use/abuse it takes from me. I bought it for the size (4lb, 5hr battery, 12" screen). It is my current laptop. I had a top of the line Compaq 15.4" that crapped out on me after a year. Previously I used: Sony VAIO (flashy but flimsy), Thinkpad x41 (solid), HP (iffy), Dell Latitude (pretty good), and another Compaq (ugh). Supposedly the Compaq quality control has improved since merging with HP. Compaq's servers are awesome though. HP has a number of laptops that score well...so it seems that they are back on the ball.
Here are some reviews that may be helpful:
PC World: Top 5 All-Purpose Laptops
PC World: Top 5 Power User Laptops
PC World: Top 5 Ultra-Portable Laptops
From the listings above, I've used (and recommend) the following laptops:
ThinkPad x60s......the gold standard for business. Well made, good performance, great battery, and ultra-portable. I used their predecessor (X41), and it was rock solid.
Dell E1505......has been well rated since it came out. I frequently recommend these for people who want something bigger than an x60s (I got one for my mother actually). Large keyboard, solid performance, and a good battery.
Alienware Area-51m 5750......grad students are not the targeted audience....games are. The only reason i put this here was because some people like it for a desktop replacement, much like the Toshiba Qosimo. It has the best of everything and is lightening quick.
-t