Hi Beth,
I too have experienced herniated disks at L4-L5 and L5-S1 with severe sciatica down my right leg. Fortunately, I was able to use yoga to heal by back pain and avoid surgery. It was a slow process and one that will keep me doing yoga forever.
First, best of luck with your surgery. Of course, check with your Doctor before beginning any exercise program. Will you be doing Physical Therapy after the surgery? If so, your therapist may be able to offer suggestions too.
I have quite a lot of information on yoga for back pain on the bellaonline yoga site, including a review of a favorite DVD by Gary Kraftsow a respected yoga teacher and yoga therapist who designed the Yoga Program used in the groundbreaking National Institutes of Health Study that proved yoga's effectiveness with back pain. The exercises are a safe, and effective for helping to stretch and strengthen the back so it may be worth a closer look.
Yoga Therapy for Back Pain DVD Review Warmly,
Martha