The Sovereign-class can separate. Presumably, most Starfleet designs are capable of it, even the Defiant-class.
Aside from a mention in one of William Shatner's novels (Spectre?), I don't recall anywhere else mentioning that the Sovereign class was able to seperate, and from what we've seen in the movies of the deflector dish area, it looks like the section between the dish and the saucer is a solid section. Plus I haven't been able to find any mentions by the designer's of the class having saucer seperation capability.