If you can get to the back of the lock, even with difficulty, by far the easiest thing to do is undo the screw that holds on the cam. That'll instantly "unlock" it, and you can open it up for further work. If you can't get to the back, before you try to drill it, you might try the old "screwdriver and vise grips" approach. It tends to be a little less messy, but it doesn't always work (and it WILL destroy the lock as badly as drilling it will). Take a large flat-blade screwdriver and jam it in the lock, then clamp on a pair of vise-grips and turn as hard as you can; use a cheater bar (aka big piece of pipe) if necessary for more leverage. Most locks will eventually fail.
If it's a round key type lock (the "high security" type), you're just about screwed. There are special bits for drilling them out, but they are expensive and usually only work once or twice before they need replaced. They're also not easy to get in some places as they are considered "locksmith tools".