Another possibility is to take No 40 from ED station to London Bridge, if you want to avoid BRail that is, then the riverboat from London Bridge Pier to Canary Wharf Pier. All the details you will need are at www.thamesclippers.com If you have a travelcard (not pay as you go) you get 1/3 off the fare. It is a bit toppy if you buy individual tickets but is more reasonable if you buy season tickets. It is, however, nowhere as cheap as using buses as previously mentioned above but an amazing way to get to work on the odd occasion perhaps (or in an emergency)