I'm actually inclined to think there isn't. The things I want from a computer and what finds success in the market don't necessarily line up that well.
I built the laptop I'm typing this on out of parts from three different Thinkpads because I wanted a 64-bit machine with a trackpoint and a high-quality 4:3 screen and nobody made one. About one in four of the programmer/IT types I talked to about it agreed that was a good use of my time and money.
It's essentially a 14" 4:3 Thinkpad T61 motherboard in a 15" 4:3 T60 chassis. They don't quite mix and match perfectly and I had to file down a couple places on the frame to make it fit. This is a fairly popular modification among enthusiasts of the classic Thinkpad line, as it's generally thought to be the best possible 4:3 Thinkpad. The keyboard came from an unknown machine (ebay) and was on a W500 for a while; I chose the part number generally regarded as slightly better than the others. The wifi card, hard drive, AC adapter and battery came from a W500. The wifi card required a BIOS hacked to remove the hardware whitelist.
Display: QXGA (2048x1536) panel, when I can find one for less than $400
CPU: If something Penryn shows up cheap or free, I'll put it in
Disk: An SSD, obviously, perhaps with a hard drive in the optical bay
Battery: I'm betting there are some modern cells with higher capacity I can put in the old shell
Pretty much everything that can be done with these has been done by somebody on http://forum.thinkpads.com, so it's pretty low-risk if the idea of a semi-custom laptop appears to you. 4:3 T61 motherboards and QXGA panels are rare and often priced higher than you would expect, but the rest of the parts are cheap and easy to come by. Careful ebay shopping may procure the rare parts for a more reasonable price.
I built the laptop I'm typing this on out of parts from three different Thinkpads because I wanted a 64-bit machine with a trackpoint and a high-quality 4:3 screen and nobody made one. About one in four of the programmer/IT types I talked to about it agreed that was a good use of my time and money.