It depends on whether or not you want a dedicated flashgun that will use the
camera's TTL metering or not.  These still tend to be quite expensive and I
am still using my old Vivitar 283 flashgun either using the flash's own
sensor or more usually on full power and using the 300D's histogram to judge
metering.  Obviously, this is not ideal if there is not time for test shots
but I still get good pictures in this way using a diffuser on the flash
head.

Roger