The Lenovo T420 can't be beaten, to this day. You can sink three SSDs in the thing (one mSATA, one primary 2.5", one in place of the ODD), it survives a beating

The Lenovo T420 can't be beaten, to this day. You can sink three SSDs in the thing (one mSATA, one primary 2.5", one in place of the ODD), it survives a beating or two, it has the legendary classic ThinkPad keyboard (later models don't) and as late models have switched to U series CPUs, the full wattage Sandy Bridge CPU in there can keep up with many of the current models. Extensibility is not bad with an eSATAp port (or two if you dock). The dock has two DisplayPorts, the laptop has one. USB3 can be added via an ExpressCard. The only other possibility I would entertain is the new Dell M3800 developer edition. The step up is significant: it has a quad core i7-4712HQ and Thunderbolt and 4K screen as an option. While even a well pimped out T420 is well below $1000 (starting at a few hundred, even), this one will run to $3K and more if you pile on everything. I'd get it if I needed Thunderbolt bandwidth but otherwise just go with the old.