Vote for the Dell Latitude E7470 series here. They are sleek, not insanely slim like some, but definitely ultrabook thin. Upsides are high-res and touchscreen, 4G capability, upgradable RAM and SSD (a least on the 7450, haven't gotten a new 7470 in yet. The best part is the docking support. I know that you can plug in USB 3 "docks" or some thunderbolt docks, but nothing beats dropping your laptop into a dedicated "real" dock/port replicator and everything just works at full speeds. Multi-monitor and dual-displayport capability. Battery life is great.
Downsides are that they are not unibody aluminum and the price ($1500+). They are not cheap. You pay for it. But it's a damn good machine for the money.