[App_rpt-users] SIP VoIP for Asterisk

I'm thinking of adding some type of SIP trunking or other VoIP service provider to my ACID Asterisk system to support in/out bound calling. I've read some emails on the app_rpt reflector with names of providers mentioned, but I am looking for recommendations, as there are zillions of VoIP providers out there. This is going to be used very sparingly so least-cost is a good thing, but good reliability and no bombardment with email adds by the provider is desired too. I can easily get by with a single number, but may want to add additional DIDs later. Thoughts? Bill