I also vote for In Sheep's Clothing as being an invaluable resource re: sheep breeds.
But I am a little bored here at work, so here is some info!
Merino - the finest and softest of the sheep breeds. Bred in Spain, where it was illegal for a while to export them. Short staple length, high crimp, fast to felt. The crimp of the merino also makes it one of the most elastic of the sheep breeds.
Rambouillet - a French breed decended from a herd of merinos either purchased by or gifted to King Louis XVI by the king of Spain. Like merino, rambouillet wool is very fine and soft.
Corriedale - a medium-fine wool, suitable for beginning spinners because its staple length is not as short as merino. (Other medium-wool breeds: Finn, Polworth, among others)
Cormo - corriedale/merino cross, with qualities of both breeds.
BFL (Bluefaced Leicester) - English longwool breed with a surprisingly soft handle. Has a slight sheen/luster, as is typical of many longer-stapled wools.
Cotswold - English breed with a long staple and low crimp, which gives the wool a wavy/curly appearance.
Lincoln - English breed with long-stapled, lustrous, hard-wearing wool. (other long-wooled breeds: Romney, Border Leicester, among others)
Icelandic - double-coated sheep. Outer coat is good for rugs and is hard-wearing, inner coat is next-to-skin soft.
Jacob - multihorned, primitive breed of sheep (seriously, they are amazing-looking) with spotted black/white fleece. Medium-fine wool with some kemp (hair-like fibers) throughout (varies - depends on the individual animal).
CVM (California Variegated Mutant) - decended from Romeldale sheep, with a fleece that varies from white to brown to black.
Course wool breeds include Scottish Blackface, Cheviot, Black Welsh Mountain, and Karakul. Course wool is great for making rugs and very-hard-wearing outer garments.
Huacaya Alpaca - New World camelid bred for its fleece by the Inca. Baby alpaca is free of guard hairs, which increase in number as the animal ages. Alpaca is seven times stronger than wool and three times warmer. Most alpaca fiber is not as crimpy as wool, so it doesn't have the "memory" and elasticity of wool and tends to drape.
Suri Alpaca - type of alpaca with a silky, lustrous coat.
Llama - New World camelid bred by the Inca as a fiber and pack animal. Larger than the alpaca. Llama fleece is not quite as fine as alpaca, and is likely to have more guard hairs.
Vicuna - New World camelid. Its fleece is extremely fine and was once reserved for Inca royalty. It was very difficult to domesticate, however, which is why it was nearly hunted to extinction for its fiber. Smallest of the New World camelids and endangered. I believe vicuna fiber is still illegal to import, though their numbers have recently increased and there are a few being raised in the States.
Guanaco - largest of the New World camelids. Fleece comparable to the llama. Difficult to domesticate.
Camel - sheds its downy undercoat periodically. Camel down is very soft and fine, suitable for next-to-skin items. Camel hair (the outer coat) is often used in the Middle East for rugs, rope, and was historically woven into a coarse fabric used for tents. Camel down fiber has been compared to cashmere in its softness.
Cashmere goat - not actually a breed of goat, but a hair type bred in goats. The cashmere that we know is actually the undercoat...the long guard hairs must be removed. The undercoat is fine, very soft, and strong.
Angora goat - produces mohair, which is a long, lustrous, strong fiber. Mohair is very lightweight and does not wrinkle or crush easily. Teased apart, mohair is cloudlike and soft.
Angora bunny - Angora bunny fur is very soft, and finished items have a distinct halo. It is very lightweight and is seven times warmer than wool. It does not have the elasticity of wool, however, so produces a drapey fabric.
Bison, Musk Ox (Qiviut), and Yak - like the camel, the commonly spun fiber comes from the downy undercoats of these animals. Extremely fine luxury fiber.