One of my easier, but stil impressive tricks is to be playing a gig and order a drink while playing. They hand me the drink, which I consume with my right hand, while I play legato with my left hand. It's quite impressive to people that don't know how easy it is.

A funny looking trick that's pretty impressive is to purposefully drop your pick while playing, but make it look like an accident. While bending down to get it, set your guitar on the back of your neck and play legato while reaching for the pick. This basically looks like your guitar and left hand stay stationary, but the rest of your body moves while you are still playing. This is a bit harder to coordinate than the other trick, but still not all that hard. Make sense?