I love when musicians dabble in the visual arts. Being married to both a musician and an artist, I understand that creative minds sometimes need multiple types of outlets for their creativity. Paul McCartney (who is my favorite Beatle - I've seen him perform twice!), is also an artist. You can see several of his paintings on this site (which includes information from a catalog of McCartney's 1999 exhibition in Germany). I really like Paul's style as well. One of my favorite paintings by him is Yellow Linda with Piano (1988, shown below).
mentions that he began to make computer art when he was on tour in the late 1990s.) Anyhow, you can see some of Ringo's art on his official art website and form your own opinion.
As for George Harrison, it doesn't seem like he took much interest in the visual arts. But hey, George can make the decorative arts rock out like no one else can (as we can see in his totally awesome music video "I Got My Mind Set on You"), so hey, that definitely counts for something.
Do you know of other pop musicians who create visual art?