We just got these Bed Tents for the kids because they've been really into the concept of "camping" and building forts.  I found them online at Target and they are made by Pacific Playtents.  They got some good reviews on Amazon so I thought I would give them a try.  They really are cute and they are very sturdy and easy to set up (took me about 10 minutes).

The bed tent fits a regular twin bed.  You get two long bendable poles that you thread through to form the tent.  Then it velcros to a fitted sheet (included) and you are all set.  Each design is different and they have little vented windows and doors with velcro that you can open & close. . We got the Country Cottage Tent for my 6 year old daughter and the Tree House for my 4 year old son. 

Kind of a cool little fort that makes bedtime fun.  They set up their stuffed animals and have a flashlight sometimes.  I got ours for about $45 at Target Online (I don't think they carry them in their stores).  They look to be a little more right now but if you shop around you might be able to find them a little cheaper.

All in all - I'd recommend!  Very cute and the kids are having a lot of fun.  AND - they actually look forward to going to bed!