Slugs don't like crawling (sliming? oozing?) over copper. I've seen ribbons of copper and other types of copper bariers sold in gardening stores, but I usually just go to my local hardware store and buy a few feet of thin, non insulated copper wire (8 gauge wire, I think, is what I usually bought). I then bend them into loops and place the loops around the veggies I want to protect. This has worked pretty well for me, and is has definitely been a good way to protect small, young plants from slugs.
Beer traps are also very effective, and I usually use a few of those too, but they tend to catch lots of other crawling bugs. Also, one of the most disgusting gardening tasks I've ever done was empty out a trap full of week old beer and dead slugs. Of course, I did dump it into my compost bin.
One other thing I've read about beer traps is that the non-alcoholic beer is better for baiting than the real stuff. I've never been able to tell that much of a difference, but I can usually find the non-alcoholic stuff on special.