Slugs - homeless snails.
One rainy summer my neighbor's geese got loose and invaded my yard. In the few hours they were here, they gobbled up all the slugs I had been struggling to control. Unfortunately, it seemed that for every slug they ate, they left 5 piles of goose-poop. Everywhere.
The cake-pan of beer (sunk into the soil up to the rim) works really well. As Mr. Lowenfels says, locate them away from the garden, and they will draw slugs by the dozen.
Something else that I discovered by accident works to keep slugs out. Using 55-gallon drums cut in thirds as raised-bed containers is pretty common. I acquired several that were rusty. I hesitated to paint them because I didn't know what paint would be safe to use in the garden (plus it was time to get plants outside), so I left them rusty. Slugs will not climb up the rusty surface. I later got some that were newer and still had nice clean painted surfaces - the slugs climbed right up and made themselves at home.