In Ehrman's How Jesus Became God, he says that when it comes to traditions about the life of Jesus, the earliest sources we have (besides Paul's epistles, which don't say much) are GMark and GMatthew/GLuke, which he breaks down into Q, M, and L, as well as the later GJohn. But he also says:

There are a couple of Gospels that may provide us with some additional information—such as the Gospel of Thomas and the Gospel of Peter, both discovered in modern times—but at the end of the day they actually do not give us much.

But after a cursory skim, courtesy of gnosis.org, it seems to me that Thomas and Peter are ripe with tradition on Jesus' teachings and death (respectively). Why aren't they more often given equal weight when it comes to weighing early traditions about Jesus? And besides those two, are there any other Gospels that are thought to date to around the same time as the canonical ones?