Google Earth's one option for looking up runs. Another resource is obviously the London A-Z, but even better than that (albeit a bit more expensive) is the Greater London A-Z on CD-ROM - goes out to the M25 and a bit beyond in certain places, and you can quickly and easily plot routes to work out distances of on-foot connections and stuff. It's £34.99 including VAT, possibly plus a bit for postage, and it's here:
http://www.a-zmaps.co.uk/asp/details.as ... stpostage=
Tell them I sent you.
They'll probably say "Who?"
Also, I find the Spider maps excellent for bus routes - I painstakingly compiled them all into a 90MB zip file which I reckon is quite handy.
http://www.busmap.org is also brilliant for timetable information (and worth using in conjunction with the spider maps, which IMHO are much more user-friendly than the maps on there).
Also, the "realistic geographic" map is great as a quick guide for which walks are easy to do. Geoff did have it on his "sillymaps" page on his site but big bad evil people forced him to take it down, but I'm sure if you ask nicely he'll tell you where a mirror of that page can be found.
And yes, the way out map is good too. As is knowledge of where the cross-platform interchanges are.