First John 1-5, Second John, Third John, Jude, Revelation 1-22

First Letter of John contains classic John themes on light and darkness.  It warns about the Antichrist (and in that sense, aligns perfectly with both the gospel and Revelation).

Letter of John 4:10, interestingly, is a striking parallel to Gospel of John 3:16: "In this love, not that we loved God, but that he loved us and sent his Son to be the expiation of our sins.

Second Letter of John includes an emphasis on "the truth," a term Pilate uses in Gospel of John.  It also features the Golden Rule.  With three separate letters to it, clearly Jesus said this one and it left as powerful an impression on his followers as his death and resurrection.  It's also the clearest break in theology from the Old to New Testament.

Third Letter of John generally addresses those in the Church who are proving useful as well as those who aren't.  The terms "beloved" and "truth" are used, more links to Gospel of John.  I might be wrong, but it's the shortest book (so-called) of the whole Bible.

Letter of Jude, which may be ascribed to Judas/Thaddeus of the apostles, speaks of biblical lore and bad apples.  Although it spoils the running countdown of the Bible featuring exclusively material ascribed to John, it also serves as an excellent segue to Revelation.

Concerning Revelation of John, I won't go into too much detail about it here.  The basis for the popular turn-of-the-millennium Left Behind series of novels, it's classic apocalyptic literature that has previously noted parallels in the Old Testament, though itself remains the most famous of them (the Four Horsemen, the pale rider called Death among them, as well as God described as the Alpha and Omega, the beginning and the end).  It may also be a pastiche on John's prediction for the fall of Rome, much as the earlier versions were of Babylon.

Interestingly, however, Revelation begins as a letter, and various congregations are addressed.

And finally, to close out my notes on the Bible, it only seems fitting to point out the final slandering of Balaam.  Seriously, the dude was to my mind a pretty good guy.

But perhaps you ought to read the Bible for yourself to decide.