There's a great book on the topic of sheep breeds and the uses of their fibers -- In Sheep's Clothing: A Handspinner's Guide to Wool. This book is very useful for spinners and felters, since it shows the fiber, discusses its uses, and also discusses facts such as fleece weight and fiber softness.
The OK State Breeds of Livestock website covers many sheep breeds, but each entry may or may not discuss fiber use.
I noticed under Finnsheep, for example, they mention the micron count (diameter of an individual fiber) but not the use. Here's a table of micron counts and the softness of the fiber that you can use to apply the OK State information to the feel of the fiber.
What I really like about In Sheep's Clothing is that it shows you a picture of the lock -- so you can visually get a feel for crimp and staple length for each breed. But, it doesn't have pictures of the sheep, so I go to OK State if I want to see the actual sheep.
If felting's your thing, see Pat Spark's Favorite Wools for Felting.
There is a German website (in English) of many of the European
sheep breeds at the EAAP Animal Genetic Databank.
Rare Sheep Breeds
If your focus is rare breeds of sheep, The American Livestock Breeds Conservancy has a very good website on rare breeds in the USA.
There are many farms working to preserve historical breeds; some on the web that are working to preserve the extremely rare Hog Island Sheep breed are Accokeek, Gunston Hall, and Mt. Vernon.
Interweave Press, publishers of Spin-Off magazine, did project
Save the Sheep, featuring finished projects made from rare breeds from all over the world.
The United Kingdom's Rare Breeds Survival Trust lists the
breeds that are rare in the U.K.
Rare Breeds Canada lists the breeds that are rare or of interest in Canada.
For related topics on this blog, see the Fiber topic.
Also see the entry, Do Soay Sheep really shed their wool?
posted 14 October 2007 at http://askthebellwether.blogspot.com/