I haven't found an image that I like that is subtle enough to use for the home screen. However, I use a photo of my partner as the standy screen on one of my 7290's (she's a belly dancer):
...and the Millennium (an old Chris Carter TV series) logo as the standby screen on my other 7290:
It would be nice to be able to pick color schemes to match the images better, but that's definitely one of my bottom priorities for new features on the Blackberry.