X1900 series cooling -
ATI stock cooler - it's cooling ability holds up well even against aftermarket cooling, it does exhaust hot air outside of the case, it's noise is decent at low speeds but awful when ramped up to high speeds
Zalman vf700 - inadequate cooling for the X1900 series
Zalman vf900 - some people have their best results with the 900 (but many have better results with the Accelero X2 or even the stock cooler,) some early reviews were misleading, it can be used later on on a different make or model of card, it looks good, it does dump it's hot air back into the case, it's quiet at low speed, it's not much louder at high speeds, it is hooked directly to a molex (so it can't use the card fan header and ramping.)
Accelero X2 - it may be the best available aftermarket cooler, it probably won't work on your next card, it's bulky and not that attractive, it also does dump it's hot air back into the case, it's very quiet at all speeds, it hooks to the card fan header so it can use the card's fan ramping, it is cheaper than the vf900, it can be difficult to remove later on if care isn't taken when installed.