Have a look at Asics, New Balance, brooks and saucony. They might not intially be the popular brands that you might have heard of like Nike and Adidas but all four are trusted brands for long distance running. Get a bit of advice from specialist running shops. Trainers now have so many different fits and specifications. Also take along your walking socks when you go for a fitting. Runners tend to wear thinner socks than walkers and it can really make a difference.