I agree with most of the ideas here...B12, dryer sheets, donuts in any standing water you can't dump, etc.
I have had a "Black Hole" for about 3 years now, and it's full of mosquitoes quite often (as well as other bugs).
Oh, and I also use dryer sheets to keep mice out of stored vehicles (boat, trailer, etc.)
Here's a good site that has both the Black Hole and bat boxes...Well, in Australia anyway. I purchased mine in the US, but I can't remember where I got it. If I remember, I'll post it up.