This is a hybrid salvia, with one parent being Salvia leucantha 'Midnight' and the other possibly being Salvia elegans. It is smothered with inky-blue flowers in autumn and early winter, and has a nicely textured leaf, with a slightly greyish look. It grows to around 1.5 m - 2 m tall and as much or more wide, forming a domed shape, so it does need a fair bit of space - I don't recommend it for small spaces. Like most blue flowers it looks good with almost any other colour in the autumn garden - pinks, cerise, burgundy, silver, orange or yellow. In full bloom, it is breathtaking. However, as it has a shorter flowering period than some of the others, you need to consider if you have the space for it. Its ultimate size can be controlled a little by cutting it back by half around January. The old stems should also be cut to the ground in August, when the new growth starts to emerge at the base. I also chop out some of the clump every year at this time to reduce its girth. It is drought tolerant and also is said to be able to cope with some level of frost.
Postscript: I eventually took mine out as it took up too much space and didn't flower for as long as other salvias. 'Blue Abyss' has similar coloured flowers, is a bit more compact and blooms for a much longer time.