Well, I'll say it's a Geranium (cranesbill geranium). A lot of these in cultivation, I couldn't say which.
Yup! Cranesbill of which there are many. I have the same purplish one as you and it does beautifully. I also have a small, lower growing pale pink one. The are very easy plants. Check out the link below, or just type in cranesbill geranium and you'll find many links. http://en.wikipedia.org/wiki/Geranium barb
Likely Meadow Crane's-bill Geranium pratense, common in cultivation, or Geranium 'Johnson's Blue' (sterile hybrid Geranium pratense × Geranium himalayense), also popular in cultivation. http://ip30.eti.uva.nl/BIS/flora.php?selected=beschrijving&menuentry=soorten&id=3177
I am not sure whether Geranium himalaiense could be involved, but Geranium pratense has very different leaves. A German page with lots of Geranium cultivars can be found here: http://www.sandfrauchen.de/07_geranium.htm. Another even bigger selection of cranesbills can be found from this Austrian page: http://home.eduhi.at/teacher/geranium/profilstart.htm.
