Inov8 Mudclaw 330s.
Inov8 Mudclaw 330s are my favourite hill running shoe. I've bought about 4 pairs in a row as its difficult to imagine a better shoe. (Although the new Mudclaw 300s look promising and I might try them out next time I need new shoes.) Before Inov8 came along Walshes were pretty much the standard fell-running shoe, and they were good. They were flat and minimal and had really good grip, which was ideal for tricky footing. Then along came the Mudclaws which have better grip. As their name suggests they can get you up steep muddy ascents without your feet slithering around. Likewise, coming downhill, they give confidence. Your foot still sits low in the shoe, like it did in the Walshes, making you less likely to twist an ankle, but the Mudclaw holds your foot better. If you have to run on a stretch of metalled road, the Mudclaws are more comfortable too.
They also cross over well to cross-country running (particularly on gnarlier courses) so you don't have to invest in spikes unless you're taking your cross country very seriously indeed.
Visit Northern Runner to view their full Inov8 range of running shoes.