Grumpy_Mike:
I don't think there's any with more than 8-bit PWM resolution.
Yes there are:-
The TLC series for a start, TCL5940 the old favorite and then there is the easier to use TCL5945 and TCL5947 these are 12 bit PWM with an SPI like interface and constant current outputs.
Yes, of course....but they're not really "similar to the ws2801". The amount of wire you'd need to make a long string of RGB LEDs using TLC5940s is ridiculous.