Well, you're going to get a bunch of opinions here.
If you want a reliable provider with E911 service and low, per-minute calling rates, many of us use Callcentric.
For example, see their rate chart below. Their E911 service is $1.50/month, but they now have a "seldom used" plan, for only $1.95/month, that includes E911. So, it's only 45 cents a month more, for 120 minutes per month of outbound calling.