Also, look into the neo900 project and Pyra. Neo900 is trying to upgrade the n900, and Pyra is the successor to Pandora, which is a pocket computer in a semi-similar vein to the old nokias. Neither is finished, but they're worth a look.
The neo900 makes me sad, because it's basically my ideal phone, but the price is just too much for me. I know it's not their fault, the low production quantities will do that, but still. It's an updated n900, with a fully FOSS stack and an isolated baseband to boot... awesome.
Plasma Mobile and Tizen are my only hopes for getting a non-Android Open Source OS on my phone.
The other project was called Moblin. It was an Intel project.
It's a shame the N950 never got a proper release. The N9 got praised highly on release, but the N950 would've been the true successor to the N900.