Fill a containers with beer to about 5 cm below the surface. Bury the containers in amongst your plants, especially where you know snails and slugs are active, make sure that the lip is at the level of the soil. The slugs can slither easily into the bowl and for some reason seem to be attracted to the smell of the beer. When they go in, they get pickled and die.
If you want something fancy you can get "Sunflower Slug Trap" or "SlugX"