Check out the Nikon SB-800 flash. Very powerful with many features for the Nikon and yet compatable with the Canon...
That's a bit of a "yes and no" situation - although a Canon will fire a Nikon flash, (and vice versa) you will NOT get TTL flash metering.
I recommend you look at the Metz models with the SCA3000 system - the bottom section including the foot of these flashes is detatchable, and thus you can fit different modules to them in order to add dedication to most cameras.
If you aren't interested in TTL flashmetering, then there is absolutely no point getting a top of the line dedicated flash - and you could consider the recently reintroduced Vivitar 285HV. It is equipped with auto thyristor and full manual control.