Two recent studies have just been published on exercise and back pain. One was published today in
Annals of Internal Medicine, touting the benefits of yoga:
http://www.annals.org/cgi/content/full/143/12/849
Another a couple of weeks back noted that ancillary exercise--like the running and walking Dave was talking about, was more effective in alleviating pain than back exercises. Unfortunately, I can't find the link for this one.
From personal experience, core exercises, particularly those using a Swiss ball, can be very helpful. These might have to wait until after the pain is gone, tho.
I found that all of the standard back stretches were helpful to me when mine was hurting. Here's a link that just adds a few more stretches to Dave's list:
http://www.nismat.org/orthocor/progr...ck/backex.html
Good luck with it. It's a bitch.