Evangelical Free Church of America
, for one.
The megachurch my family and I have been attending for many years is one of these.
It's an "association of autonomous churches". Basically, that means once you've seen one of them, you've seen one of them. That statement of faith is vague enough to encompass a lot of different things, and both Calvinism and Arminianism coexist in it (my church is officially neutral, but I've seen a few of the leaders try and promote various Calvinist books). It began as an offshoot of Lutheranism, but that's barely recognizable now in the case of many of the churches.
The one I attend is a middle-of-the-road Baptist-type place (1 hour sermon + praise band, no charismania, monthly memorialist communion in little plastic cups, baptism is downplayed to an extent and is only for adults, nothing else in the way of the sacramental, liturgical, or mysterious, but it does have all the things that attract people to megachurches including small groups, Sunday school, youth ministries, disability ministries, etc.) It's also about as ethnically diverse as you can get, which is pretty cool. Lots of Hispanics, Liberians, etc.