I often use this site http://www.bikely.com/ I do the same route to work - I avoid the main streets, so it takes a little longer but it is a genuinely nice bike ride. My route is Bellenden Road, then across to Cambewell - take Benhill Road, round Addington Square and then along Bethwin Road, connect to Cooks Road (Kennington), across Kennington Park Road, up Ravensdon Road, Milverton Street, then Courtenay Street to Black Prince Road which leads you straight to Lambeth Bridge. Sounds complicated, but take a look at an A-Z. Its all bike paths. Order the free bike maps from TFL website as well. Good luck!