I use the cut-off bottoms of soda bottles, large or small.
Many say that you should sink the dsaucer into the gorund a little to make it easy for them to climb in, but I see they can crawl right up onto my porch so I'm not so solicitous to them.
They still find the beer.
I put out a bunch of beer saucers before an early Spring thaw, and caught hundreds ... then a cold snap turned them into slugsickles.
