Dennis Wilson would've been 64 today. He was a sensitive guy, at first overshadowed by the other Beach Boys (he didn't sing lead vocals for years, and wasn't the primary songwriter on any songs they recorded till 1968).
Like his brothers, he had a deep spiritual side, which you can hear on his original Christmas hymn. (This song is so relaxing and warm I included it on my '06 compilation, Have Yourself A Mellow Little Christmas. Stay tuned -- it's coming in three days.) This was recorded for 1977's aborted album Merry Christmas From The Beach Boys. Once it was clear that album wouldn't be completed, Dennis set it aside for his own second solo album, also never completed.
Also from 1977 is a PSA Dennis recorded, featuring part of The Beach Boys' recording of "Santa Claus Is Coming To Town." Alongside the buy link down there, I've included a link to donate to Toys for Tots. (The 1977 toy drive apparently was in Eugene, OR, headquartered at The Crystal Ship, a now-defunct record store. The whole group also recorded a new version of "Little Saint Nick" for that, which I haven't included here.)