Andi, I agree with Toni that Blue Girl is the bluest of them all, and it's available from lots of own-root nurseries.
I do have a Lady X that's even bluer, but it's an old grafted plant and I've never seen an own-root Lady X that looked good. It's one of those roses that doesn't grow well on its own roots.
Here's Blue River. I think it's one of the prettiest of all the "blue" roses.
