If the rim is only slightly bent, you can fix it, but it will never be a good wheel. If it is throughly bent, just forget about it. You can probably reuse most of the spokes, the hub, the tire and the tube though.

You might check the instructables web site for ideas of what to do with a unusable rim. I saw one person had made a wetsuit hanger out of one.

Make it into furniture like the stuff found here:

http://www.bikefurniture.com/

If its badly bent (ie it won’t go round in the frame) you can’t do much, but some alternative uses are:

Crayfish nets! - the rim can be used to suspend netting in to catch crayfish.
(invasive American crayfish destroy our river biodiversity)
If it has a dyno hub you can straighten it enough to make a wind generator by covering the spokes in tape so they look like windmill blades.

You can also buy a second hand wheel from one of the many bike recycling projects in the UK
see www.bikerecycling.net for your nearest one

If it’s only slightly bent, you could make a pot rack out of it - http://cache.lifehacker.com/assets/resources/2007/07/bike-wheel-pot_rack.jpg

they can be rebuilt, perhaps a new rim is required and a few replacement spokes. All the rest should be OK.

How about a bike rim chandelier?
http://www.craftster.org/forum/index.php?topic=24677.0

Or a bike rim candle chandelier
http://www.diynetwork.com/diy/cr_candles/article/0,2025,DIY_13748_5282897,00.html

Clean it up and use it to dry all your socks and pants.