The temperature depends on the yeast. All of the yeast manufacturers will give you stain specific fermentation temperatures.
As an example, from the Wyeast and White Labs websites:
YEAST STRAIN: 1968 | London ESB Ale™
A very good cask conditioned ale strain, this extremely flocculant yeast produces distinctly malty beers. Attenuation levels are typically less than most other yeast strains which results in a slightly sweeter finish. Ales produced with this strain tend to be fruity, increasingly so with higher fermentation temperatures of 70-74°F (21-23° C). A thorough diacetyl rest is recommended after fermentation is complete. Bright beers are easily achieved within days without any filtration.
Origin:
Flocculation: Very High
Attenuation: 67-71%
Temperature Range: 64-72F, 18-22C
Alcohol Tolerance: 9% ABV
(Notice it tells you that the beer will be increasingly fruity with higher fermentation temperatures of 70-74 degrees).
and
WLP001 California Ale Yeast
This yeast is famous for its clean flavors, balance and ability to be used in almost any style ale. It accentuates the hop flavors and is extremely versatile.
Attenuation: 73-80%
Flocculation: Medium
Optimum Fermentation Temperature: 68-73°F
(20-23°C)
Alcohol Tolerance: High
In general, the lower temperatures produce the "cleanest" flavor while fermenting at the higher range of the yeast strain's optimum temperature will produce more fruitiness depending on strain.
I ferment most ales at 62-64 degrees, but will go higher for certain yeast strains.