I've been using this wireless network camera for about a year now. It's a Planex CS-W04G
At about $51 on Amazon, it's the cheapest wireless network camera that I've been able to find. For some reason the tag line is Designed in Japan, which I find cute.
It also works great with sensr.net via the built in FTP functionality.
Here's a sample image from mine under relatively low light conditions, about an hour before sunset with east facing windows.