About 15lbs is the race limit and, allegedly, weight has to be added to some of the pro bikes to reach that limit. But these sorts of weights tend to be the playground of the dedicated amateur, the wealthy hobbyist and, obviously, sponsored pro riders.
On a more realistic financial level then anything sub 9kg/20lbs is light and 10kg seems to be the 'claimed' weight of a lot of lightweight production bikes. Though these weights are often measured without pedals. Personally I'd class anything sub 25lbs as light, sub 30lbs as ok and sub 35lbs as liveable for a purpose, ie commuter.