I just switched our ISP to WebPass from Comcast. We now have dedicated bandwidth and we should have a much more reliable connection for our VoIP phones and Skype video calls.
All ISPs give you at least 2 DNS servers to use when you configure your router. However, I have simply been using the Google DNS servers. First, they are super easy to remember:
And second, I trust their reliability a lot more than I do most ISPs. If you ever do run into problems with domain names not resolving, you can always switch back to your ISP’s DNS servers. But I doubt you will. These are way more reliable than any ISP I've ever used.
Speaking of which, I keep a Google spreadsheet with all of my ISP info in it, just so I'll have it in a handy location should I ever need to reconfigure or replace the router.