Features of a Good Bird Nest Box: This infographic has tons of information. Cornell Lab of Ornithology
owl boxes | Owl Nest Boxes | Wild Route Environmental Consultants
Dove and robin nest box
I dunno about how easy these would be to keep clean but they'd probably be cheap enough to make.
How to build nesting boxes out of one piece of plywood
British Trust for Ornithology - DIY instructions for small hole nest boxes ideal for blue tits and great tits
Mourning Dove Nesting Box- I need one of these. I love them.
How to build nesting boxes for your chickens using materials you have around…
20 Easy and Cheap DIY Chicken Nesting Boxes
How to build your own rabbit nest boxes, very good instructions