I leave them until the clumps spread and then divide them.
But there are so many varieties including some lovely blue ones so why not get some different ones instead of propagating?

Like Stera, my clumps spread on their own, and your small pale pink one seems to be doing that already. But now is a good time to take cuttings, and you can just remove the flower to save the plant's energy.

Thank you both very much. I am looking at getting some new Geraniums. I find these particularly good because they don't grow too high. They are in a west facing border and I really struggle with taller plants here as they bend almost to the floor to reach the light. If either of you could suggest some lower growing geraniums I'd be very grateful. Thanks again

I'm very happy to tell you about the ones in my garden, tho' you might not necessarily have the same taste! However, Rozanne is a lovely blue and long-flowering, but it does need about 2ft diameter circle (mine has self-seeded); G. Black Beauty has navy blue flowers and very dark leaves which I love (and has also self-seeded). I'm fond of the G. sanguinem ones which mostly have deep pink flowers - whites are rare - they are VERY low-growing, 3" - 4" and only spread very slowly, and also have Mrs Kendall Clark which is pale blue. The G. psilostemons are very attractive, particularly 'Ann Folkard', deep pink with a very dark centre (I don't have this one, and it might be taller than you'd like). Have fun :)

It sounds as though your border is in shade a lot of the time if your plants are leaning to the light. Some geraniums are more shade tolerant than others. Could I suggest you look at the list of shade loving ones you will find on Long Acre Plants website? Its a useful place for ideas as there are pictures as well as plant names. There are several other websites too with heaps of suggestions. Just Google Geraniums Shade.
Most geraniums are bare in winter but there are a few evergreen ones and there are some that flower early in the season.
I too was going to suggest G sanguinium varieties for the very front of the border but they are sun lovers. I do have a white one but it doesn't flower as freely as the pink ones for me.

Thank you all for answering my question. I hadn't realised how many different Geraniums there are. I'm going to have a good look through them all, especially the ones you've suggested and I'll let you know when I've decided.