I've just bought an Axis network camera for a project at work. The thing is basically a embedded linux system with a camera and wired and wireless network adaptors. You can write your own bash scripts and schedule them in a crontab or fire them off a closing contact or on screen motion. It uses busybox so you have the usual bunch of built in commands. Or if you need more flexibility you can cross-compile stuff (it's ARM at heart).

Axis provide quite a few helper applications for grabbing video, stills and audio, automated ftp, http and email transfers. The script I've written grabs a frame every 5 minutes, ftp's a timestamped file to one ftp server (which we will use to build a timelapse video with) and a file called latest.jpg to another ftp server which will go on our website.

The cameras aren't cheap, the one I'm working with is over £200 for a VGA resolution one (albeit with a very good CCD so very little noise and excellent low light performance). There are some really nice ones about the £500 mark with C and CS-mount lenses.