Try
where-can-i-live.com, I think that's the slickest site with most features.
CommuteFrom does quite a good job, but only includes zone 1 underground. You should bear in mind though that the Overground goes into Euston which is very close to MC and would get you further out inside your 30 mins.
Here's a funky map which shows the Tube map according to travel time - everywhere in the middle 3 circles will be within 30 mins.
There are some very cool interactive maps
here, but unfortunately can't be changed from being centred on the DafT offices.