I like the Renegade Cozy Partner Model 50
http://www.emergencysec.com/holster12.html
Ankle holsters are definitely a compromise but I think they have a valid place for both primary and backup carry.
Pros
1) The last place most people will look to spot your weapon.
2) Usable with attire that wouldn't allow other types of carry, e.g., business casual.
3) Best way to access your weapon quickly and discreetly when seated, e.g., when at your desk, or eating, or belted in your car. This factor is often overlooked by those who are standing up when conducting the majority of their interactions with people.
4) The weapon is accessible no matter how you land when you have been knocked on your ass and you don't have to sweep yourself to engage your opponent. Also eliminates the possibility of breaking ribs from landing on your piece. Another often overlooked asset.
5) Huggers and gropers will not find it. For those of us who have to do a lot of interaction with touch-feely women, this is a significant asset. Also applies if you are concerned about a "bump frisk."
Cons
1) Accessing the weapon while standing up is more difficult and slower than most other carry systems.
2) The weapon will pick up more trash than with a belt holster although probably on a par with a pocket holster, which is more of a trash magnet than people acknowledge.
3) The weapon can be visible when you sit down which, in some cases, is a disadvantage.
4) Can be easy to bang the gun into things when moving.
5) Not particularly usable with tighter pants.
6) Running can cause the gun to come out with some models of holster.
7) Requires significant practice, both initial and ongoing; more than any other draw system, except a Level III duty rig.
A good technique I learned from Lenny Magill is to wear the holster on the back of the ankle, as opposed to the side. This makes it much more comfortable when walking and also reduces the amount you bang the gun into things, like the door frame of your car. There is no difference in speed or accessibility of the draw.
One reason I like the Cozy Partner is that it is of nylon and elastic construction which people easily mistake for an ankle brace. Provides a good cover story should it be spotted, which it never has. I also always wear black socks with it as further visual camouflage.
You have to try a good ankle holster out for a while to see if it works for you. The only thing I would really avoid is a calf strap. These can lead to blood circulation problems in the lower leg if they are tight enough to be effective.