With iOS 5, you can now customise all of your alerts tones.
There are some great tones in the R2D2, quotes from Anchor Man and even Jaws.
To get there, load up the iTunes App on your iPhone, hit the more tab (see above) select tones, scroll down past all the Ringtones and your there ! You can sort from the top between Features, Top Ten and Genres.
Go end explore, I promise some of them will bring a smile to your face !