LiMo Foundation
The Linux Mobile Foundation looks good, but where is the source code? Verizon Wireless just joined...
Android
Is this the same as Android? No... that is the Open Handset Alliance. From what I can tell, Android isn't completely open source.
OpenMoko
This is truly open source!
Internet Tablet OS
I love this operating system! It is open source (aka maemo.org), and is available on the Nokia n-series.
Mobilinux
Mobilinux is from MontaVista Linux, but again, where is the source code? Hmmm.