Shred is really good. Some people find it very hard at first, but if you are reasonably fit and have been used to running it should be fine. I've been amazed at what it does for me, considering it's only 20 minutes long. It tones bits that running never touches!
Shred is DVD with 3 x 20 min(ish) routines combining cardio, weights and tummy exercises. Loads of threads about it. Think it would be good for you as the walking won't elevate your heart rate in the way that jumping jacks etc will, plus its only a fiver from amazon.
weight lifting - walking will burn calories, weight lifting will strengthen the muscles and keep your good shape.
There are free lifting programmes online (Stronglifts 5x5 is a good one) and look at exrx.net to check form (google exrx and the exercise name as it doesn't have a functional search engine). A good book programme is 'new rules of lifting for women' available on amazon. Argos sell cheap weights (get a barbell/dumbell set) with delivery. Much cheaper than a gym membership and no putting it off for bad weather.
If you don't want to fork out for weights google for weights programmes with household objects - nerd fitness (website) do a good one.
I second the 'Shred' idea. Ideally I run a few times a week and do Shred a couple of times. You might even find doing something like Shred will reduce your likelihood of running injuries by strengthening your muscles. Have you stopped running altogether or just cut down? I used to get injuries, but I changed my running style after reading a really inspiring book (Born to Run) and haven't had any injuries since (touch wood!)
About a decade ago (crumbs) I lost a lot of weight through running x4 a week, enjoyed it very much, entered races etc. Unfort I've had to stop - I was getting too many injuries. So I swapped to the gym. That was working, but now life is hoovering up my bank acc. I will have to bite the bullet and stop that. I don't propose on parking myself on the sofa for the rest of my life. I am A Walker (please not the spelling) - on average 7K on the days I don't gym. If I swap gym days for more walking days, will I lose my hard earnt smaller bottom? Ahem. A friend who is some kind of sports guru is very sceptical about running. She thinks it's what people do when they're too weak to run.