My Thinkpad T420 has been stellar. As much as I like Dell's Latitude line, the newest E6420 doesn't compare; its larger, heavier, and not as ergonomic. Lenovo also wins on keyboard; no-one tops a Thinkpad for that.
Always get onsite service with Lenovo though. There have been horror stories on the Notebookreview forums about some of the mail-in experiences.
Core i7-2600K @4.1GHz, GIGABYTE GA-Z68XP-UD5, 4x4GB G.Skill RipJaws PC1866
Corsair 650D case, Seasonic X750 Gold PSU
WD `Raptor 600GB boot, WD Caviar Black 1TB data, NEC 7200 DVDRW
2x Radeon 6970 2GB in Crossfire, X-Fi Titanium, Dell 2407WFP