If your wordpress blog is getting high enough traffic then you'll need at least a vps server if not a dedicated server.
Depending on the actual amount of website traffic your website is getting your wordpress blog can likely manage on vps hosting awhile.
But make sure you know how to manage a vps server as it's entirely different than using a shared hosting account.
You can get managed vps though for more money.
Hawkhost has good vps web servers that your wordpress blog should work just fine on.
You don't actually have to have wordpress specific hosting. Wordpress can be hosted on any web host out there.