There's not a lot of hosting companies that focus on ASP.NET hosting out there. I am the CTO of one of the first Window's based hosting companies out there so I'm a bit biased, but there's many good hosting companies out there. I know it seems weird to recommend my competitors, but I know the owners and workers at the companies below and I can vouch that they all offer good products.
Applied Innovations
CrystalTech
DiscountASP
I recommend sticking with a host that focuses on .NET as they will be able to support you better.
One of the most important things you need to look for is what application pool limits the hosting company puts at the different plan levels. Make sure to call and ask if they don't publish it, it's very important, you don't want to get a cheap plan that won't suit the memory needs of your application and have to upgrade soon after the purchase.