I paint my canvasses all the way around the edges so they can be displayed without framing. But a proper frame does give them an extra touch. It's very much like a monitor or tv-screen; the frame seperates the image from it's surroundings. I like to use a so called 'floating frame', which attaches to the back of the painting. Because this kind of frame only shows a very small edge, it provides a framework without being too prominent. The frame I prefer is black except for the front edge, which is gold or silver depending on the colours I used in the painting.