Anybody got any spiffy tricks to find the gaps in a range using SQL?

Say I've got a table with:

Start   End
    1     5
    6     8
   12    15
   19    24

I'd like to find the gaps (9-11,16-18). One other thing, I'd also like to be able to give it some limits like "find the gaps between 10-17" so it should return 10-11, 16-17, in that case. Or do I have to do this by just brute force, since I need to look at 2 records at a time?

TIA