My favorite edging is a simple trench dug in early spring when cleaning out the bed. Dig straight down with a spade to sever the grass roots, and mound the soil from your small trench up to the bed itself. It is fairly easy to maintain during the growing season and if you trench again in fall, you'll be way ahead of the game. I don't always get to that second trenching, but always wish I did. I like this method for neatness and simplicity. Tons of other choices out there, and I'm sure others will chime in.
