IME, none. There are dimmable ones, some which run on a dimmer and others which can use just a regular switch, but none which actually dim like a normal bulb. The other problem is that most dimmers have a minimum load below which they don't work, and with that typically being 40W and the CFL being less than that, the dimmer won't work anyway.
If you want dimming, forget about retrofit CFLs and go with either dimming fluorescents on electronic ballasts, or dimming 12V halogens (although they may also be banned at some point in the future). LEDs may eventually be the way to go here, but they aren't there yet (unless you have lots of money, or you want to make the whole thing yourself from individual LED parts, and you don't need lots of light).
I'm planning on converting some mains lights (3 lamp pendant and two single lamp wall lights) which are on a dimmer to use 12V halogen capsules instead. I'm making up a set of halogen capsule (G5.3) to bayonet cap (B22d) adaptors. Currently made two, and just got a 3rd bayonet cap base from a dead lamp (I'm limited by rate at which I find dead bayonet cap lamps from which I can reuse the lamp caps).
That's subjective. You would need to more accurately define which properies of a normal bulb you want to match.