When can I bottle my beer?
Typically, you can bottle an ale 3 weeks after brew day with two-stage fermentation. This schedule allows 7 days for primary fermentation, and 14 days for secondary fermentation.
Wheat beers are often bottled right out of the primary, as it's common to not worry about the yeast still in suspension. No one balks at a glass of hazy weizen.
Lagers will require up to 14+ days in the primary and often 4-6 weeks in the secondary before bottling. In any case, when the beer's specific gravity has stabilized at it's terminal gravity and it has sufficiently cleared, it's ready to bottle.
Other "big" beers can use some extended aging, possibly leaving in the secondary for several months to develop their complexities in bulk and to allow yeast, gravity, and time to round out the edges of the beer. For these extended aging beers, you may wish to add a little bit of yeast (1/4 tsp should suffice) to your bottling bucket to make sure there are enough yeast cells in suspension to carbonate the beer.