The first AKs were the "Type 1"s, followed by the "Type 2"s. They're all going on half a century old and pretty rare in the USA.
Then came the "Type 3", otherwise known as the AKM, for AK-Modernized. AKMs were made with stamped or milled receivers, fixed, underfolding, or sidefolding stocks, in the USSR, China, North Korea, Albania, Romania, East Germany, Yugoslavia, Hungary, Bulgaria, India, Egypt, and probably a few places I've forgotten.
Of the AKMs, there were a couple of short barreled versions, the Tantal and the Krinkov. There was also a long barreled version, the Tabuk.
About the time the AKM came out, Finland licensed the AK design from the USSR. The Finns did quite a few modifications to the design. They're collectively known as "Valmets", from the first Finn company to build them. Valmets are easily distinguishable by the "slant cut" receiver that angles up from the trigger to the bottom of the barrel. The Valmet in turn spawned the Israeli Galil and the South African R4 and R5. Most Galils and R4s were chambered in .223, with a handful of Galilss in .308. Valmet used 7.62x39 and .223 for most of their military stuff, but civilian-market rifles could be had in .30-06, .243, and other calibers. There was also a "Valmet Hunter" with the trigger group moved back, no pistol grip, and a conventional wrist-type stock. There were some "Hunter" clones imported from China before the Assault Weapon Ban; they are the only non-Valmet-derived AKs to use the slant-cut receiver.
In 1974 the Soviets introduced the AK-74, the major difference being that it was chambered in 5.45x39, basically similar to the US 5.56mm/.223 cartridge. In post-Soviet Europe, many of the old Warsaw Pact countries converted from 5.45 to the 5.56 NATO.
There is an AK-100, AK-105, etc., all basically AK-74s.
A few years ago the Izhmash factory began selling civilian-market rifles in either pistol-grip or wrist-stock variants, depending on where they were being sold. They offered a wide variety of military and sporting calibers, and you can buy a new one through most gun shops or sporting goods stores. The Saiga could be thought of as the "next generation" AK - almost every part is different, but it all looks and works pretty much the same.
To me, the weirdest of the AKs are the Saiga shotguns. Saiga makes AK-47s in .410, 20 gauge, and 12 gauge. The whole idea of a 12-gauge AK is simply *wrong*.
There are a few other oddballs. There was an AK-based light machine gun called the RPK, which had a "bulged" and reinforced front trunnion. This trunnion was used in the Yugo AKs, which are super-heavy-duty (and heavy) variants. The Yugoslavian army really, *really* liked rifle-launched grenades, and beefed their guns up to take the punishment.
The Romanians had a "stretched" AK called the PSL, which shot the 7.62x54R rimmed cartridge from the Mosin-Nagant. There were Chinese, Iranian, and Russian guns that were quite similar. Almost no parts directly interchange between them, however.
There were bullpup variants sold in the USA, made by Valmet or Norinco.
The Israeli Hadar II was chambered in .308, had a 20" barrel, and had a full wood stock. The Molot Vepr II is also available with a full wood stock. Some of the early Saigas wrapped the entire receiver and gas block in a plastic cover to hide the giveaway AK profile.
There were pump-action AKs for markets that forbade semiautos - originally England, then California. The PAR and PAP models were sold in the USA. In South Africa, there was the pump action H5. While the PAR basically just put a handle on the gas piston, the H5 was a substantial redesign of the AK platform.
There were some "SMG" variants, the Groza and Bizon coming to mind. Various countries had drum magazines to feed their AKs, but the Russian Bizon uses a helical magazine that looks like a can of spray paint.
There's a lot more, and undoubtedly some of the details of what I just said are askew, but it should help get you going. I never found an "All About AKs" site either...
You might get some useful information out of the "Gratuitous AK Picture Thread" which has pictures of a lot of the variants.
Gratuitous AK Picture Thread - Gunco.net