Alplains is run by Alan Bradshaw in Colorado. In addition to providing a great seed catalogue containing many western natives, his site is also a great resource for germination requirements of many plants.
Seed Propagation of Native California Plants
By Dara Emery
This is an indispensable book for those interested in growing native California plants from seed. Dara discusses numerous strategies for seed propagation and then offers a very extensive list of many native California plants with recommended seed treatment for each species.
Seed Germination Theory and Practice
by Norm Deno
This is a great resource for the propagation geek. Norm Deno describes many mechanisms that trigger seed germination. He then describes germination patterns and requirements for many plant genera, including lots of rock garden plants. He published two supplements to the first volume, which include even more plant species. These are no longer in print, but pdf versions are now available for free through the USDA.