If you have a mobile phone with Bluetooth or WiFi, you can use a program called Vectir for remotely controlling PowerPoint.

Vectir - IR, WiFi and Bluetooth Remote Control


This is really useful when travelling because you don't have to remember to bring a remote control with you. As long as you have your phone in your pocket, you won't be without a remote. I use Vectir with my Blackberry but it also works with Nokia, Samsung, Motorola and other phones.