Chris Thompson rigged up this time lapse intervalometer for SLRs made from a cell phone headset, a 555 timer, and “a bunch of electronics bits.” He threw up his HOWTO on Instructables.
While Chris’s hack makes the time lapse gear much more portable, many DSLRs have software available from the factory that let you do time lapse if you keep the camera tethered to your computer. Also, many video programs like Apple’s iMovie (at least the old version) allow you to shoot time lapse from an attached video camera or the built-in webcam. For obvious reasons, those won’t look as nice as shots from a DSLR, but it’s a good option for web video.
Below, a video of time lapse shots Chris took with his rig of some fireworks.
Time Lapse Intervalometer for SLRs with 555 timer IC [Instructables]