The best dim sum restaurants are probably located in Richmond but since we are talking downtown a few places come to mind:
-Floata in Chinatown. Very good and well priced.
-Imperial Seafood. Haven't tried it yet but have read great reviews.
-Sun Sui Wah. Again, never tried it but good reviews.
-Pink Pearl. A bit out of the way of downtown and not overly impressed.
-Kirin. Very good reviews.
You can do a search in the chat forums at
www.egullet.org OR
www.discovervancouver.com for more information.