blueSLR is a new application/dongle combination that allows you to control a DSLR using your mobile device. You plug a Bluetooth dongle into your Nikon DSLR (support for Canon is "coming soon"), pair it with your iOS device, and now you've got a remote control for your DSLR. The dongle also allows you to geotag your shots, as it adds location data.
The application is currently available on iOS devices and is reportedly coming soon to Android and Blackberrys as well. The combination of the application and the dongle is $149 (free shipping for a limited time). See below for specific Nikon DSLR models.
blueSLR for Nikon Essential DSLR
Compatible with: D3100,D5000
blueSLR for Nikon Advanced DSLR
Compatible with: D90, D7000
blueSLR for Nikon Professional DSLR
Compatible with: D2Xs,D3,D3s,D3x,D200,D300,D300S,D700
If you don't need wireless functionality, or you're shooting on a Canon, check out DSLR Camera Remote, which has a free version (the full app is $19), and has an interesting-looking iPad version coming soon:
If you have a Wireless File Transmitter, then you can apparently also use the DSLR Camera Remote software to trigger your DSLR wirelessly. This is all new to me, given I'm not primarily a stills photographer -- anyone have any experience with this app or have any other solutions to offer?