The Waldensians were a group that agitated for the Reformation. Also, within the Catholic Church there were Christians who challenged the authority of the pope and many of the RCC's worst teachings (such as transubstantiation, the veneration of images, etc.). Some of them were outspoken and persecuted for their faith, while others sort of kept to themselves and pushed for Reform from within. If you go back a bit earlier, it is easier to find real Christians--even though they may not have had some sort of identifiable "church" other than the Roman Catholic Church. For example, in the 8th-10th Centuries (if I recall correctly) and before, iconoclasts were throughout the church. Protestantism brought about the revival of iconoclasm, and for good reason--the second commandment. And so on.
That said, I should add that we don't want to be naive, here. Protestants historically embraced the view that Christian theology (and official church teaching) progressed through time. So, for instance, as controversies became urgent, the church has to clarify Scripture's teaching in order to divide false teachers from the true. So, our Christology was developed in response to the teachings of heretics, and many true Christians in the early church wouldn't have had as sophisticated and subtle of a Christology as we do today. After all, they weren't aware of how the Christological controversies were resolved. Similarly, the Protestant Reformation brought clarity that didn't exist before the Reformation. Accordingly, although true Christians had always been saved by faith alone, not all of these Christians could have clearly articulated the doctrines of sola fide and/or sola scriptura. This isn't a big deal. In fact, that's what Protestants should expect given their commitment to the historical progress of theology. So don't have too high of expectations for our brethren who lived before the Reformation era controversies. Their beliefs will often be vague and/or confused on the points in question. That's to be expected. (Frankly, Catholics have to do the same thing...the early church simply didn't hold the exact same view of the Bishop of Rome as Catholics do today.)
--Dan