There are a lot that will do the job. I've got a WGI IR4C
that I've been using just for that the last few months.
It cost about $90, and is IR flash and uses C cells inside the
camera. But I wired an external power jack on mine and can use
any kind of battery. Some people have trouble with them, but mine
has been going since last Sept with no problems. I record video
most of the time. "20 seconds with a 30 second delay"
It's 320x240 res, but it's still good enough to make out who is
there. The stills are 4 MP day, and about 2 MP for the night B/W
IR stills. Uses SD cards up to 2 GB.
The sensor is pretty good. I have mine mounted near the garage,
and it will light up on someone walking down the street, 55 to 60
feet in front of the cam. I had it light up on a crook who was trying
to break into the car across the street. That was 80-100 + feet.
Couldn't make out details on him, but it sensed him. Just too far
for the IR flash to light em up. But anyone near my trucks will be
lit like a Christmas tree, and ID will be easy. It will sense birds that
light in front of it. So for less than $100, I guess I can't complain
so far. I took it to my Oklahoma place in November, and I got
quite a few deer videos and stills and with no feeder at all.

Just planted it in a place I thought they would be running, and sure
nuff, it got a few of them.
I'm fixing to build a "deluxe" trail cam from a Sony W290. It will
do 12.1 MP, and 720p HD video. I've already bought the camera,
but still need to buy the sensor board, case, etc..
I'm in no rush on that as I won't be using it until the spring.
It will be a white flasher.. I don't want to mess up the day color
with a IR hack on that cam. It will be more for higher quality day
pix.