Personally, I hate that the rumble pack for the DS Lite sticks out of the thing when you're using it. Actually I hate that all GBA carts stick out when you're using them, but that's another story.

Enter Xyzzy, an Instructable user that came up with a bit of a homebrew mod that jams a rumble pack into the DS Lite's dust cover. The mod uses an old Pokemon cart, and the motor from a Nokia 5100 phone, meaning more than likely you won't be doing this one on your own. But it's still worth checking out how he did it.

DUY RumblePak for Nintendo DS Lite [Instructables, via Nintendo Gal]