Useful to check before heading out without waterproofs…
Rainalarm (free) app for android is very similar but it also alerts you to nasty weather heading your way. Saved me a soaking on more than one occasion when it looked nice as I put my gear on only for the black clouds to gather as soon as I got down the road.
I prefer: http://www.metoffice.gov.uk/public/weather/forecast/london#?tab=map&map=Rainfall&fcTime=1378803600&zoom=5&lon=-4.00&lat=54.65
Seems to have a larger time slot and the above link is forecasting, not just what has happened?
I am a big fan of the Rainalarm app. It has saved me a soaking loads of times.
Thanks - useful. 
Until I saw the Raintoday website I didn’t realise how simple weather forecasting should be. Basically if you check it and see that a bleeding great rain cloud has been tracking it’s way down South for the last two hours then the chances are it’s going to hit by the time you’re out on the bike. This is all I need to know as although it won’t stop me from going out if it’s going to rain it is nice to be forewarned and appropriately clothed. Compare this to the BBC forecasts- which tell you bugger all really. I guess they are advance predictions tied into the TV production timetable rather than using real-time up-to-date info.
I think the BBC gets it from MetOffice…
Tracking where it’s come is good but so often you can see the rain dissipate around London 
While I use rain alarm a lot I have found that it does sometimes show light rain when there actually isn’t any.
That isn’t to say it is a bad app but perhaps more about the state of the art of weather radar.
There is a rain alarm extension for your pc, also I have tried
There are others, just google rainfall radar.
All seem to use the same Met Office data but may filter it more or less effectively.
Sorry if this bores the pants off most people, but I used to need this type of thing in a previous job.