In reply to gcandlin: The Bat at Doveholes (Dovedale) and Thor and Kyrie Eleison at Thor's Cave in the Manifold Valley are great aid routes and a good intro to the more complicated ropework involved etc as they are on bolts.
Millstone also has some good cracks to aid but obviously show respect for other users, aid climbing is pretty slow so don't hog classic lines, going there when its wet would be a good idea (and give you something to do on a wet day!). I can recommend London Wall on aid, I did it before a Yosemite trip to hone my aid skills and it was excellent.
Most gritstone quarries should have some lines worth aiding if you want to go somewhere quieter on a nice day. You could clean up some neglected routes in the Lancashire quarries while you're at it and do us all a favour!
If you want a really memorable experience you could climb The Big Overhang at Parliament House Cave, North Stack, Gogarth and then there's The Scoop on Sron Ulladale in the Outer Hebrides, probably the ultimate aid route in the UK.