[quote=vrummage]1. Main Line
Mainline Protestantism usually refers to the oldest forms of Protestantism from which newer sects have broken off communion. In other words, the newer sects have developed from the mainline sects. The mainline sects also usually take more neutral positions than the newer sects. Usually considered mainline are Lutheranism, Episcopalianism, Methodism, Presbyterianism, and other established Protestant communions.
As Karl Keating explains in his book Catholicism and Fundamentalism, the term Evangelical covers such a broad spectrum of Protestantism to be almost entirely meaningless. Some of the mainline sects who otherwise shun the label Fundamentalism consider themselves Evangelical (particularly Lutherans and Presbyterians) while many who identify with Protestant Fundamentalism prefer the term Evangelical because of the negative connotations attached to Fundamentalist. As a rule of thumb, professed Evangelicalism encompasses more Protestant faith traditions than Fundamentalism, but many Fundamentalists also consider themselves Evangelical and prefer the term.
These are usually Protestants who adhere to the so-called “Fundamentals” identified in the early-twentieth-century by conservative Protestants in reaction to more liberalized Protestant groups. The “Fundamentals” are: the inspiration and inerrancy of Scripture; the divinity of Christ (including his Virgin Birth); the substitutionary atonement of his death; his literal Resurrection from the dead; and his literal return at the Second Coming. For more information, please see the Catholic Answers tract Fundamentalism, from which this list is taken.
Pentecostalism is a specific branch of Protestantism, like Lutheranism and Methodism are branches. Pentecostals are usually conservative, often identifying with Fundamentalists, and are particularly focused on the gifts of the Holy Spirit. The name is taken from the Pentecost experience of the Holy Spirit in the book of Acts (2:1-4).
This is a pandenominational movement, appealing to even some Catholics, that emphasizes the gifts of the Holy Spirit. For more information from a Catholic perspective, I recommend Renewal Ministries.
[quote=vrummage]I would appreciate some clarification as to what the terms mean, which denominations would be classified as such, and any resources you are able to recommend.
Handbook of Denominations** by Frank S. Mead and Samuel S. Hill