ARM has made their elegant 32-bit RISC processor core available for licencing to chip manufacturers, who have used it to produce a wide range of very cost effective microcontrollers, packed with lots of peripherals and generally requiring quite simple support circuitry to run. Easy to use, not demanding much space or power, affordable, and bursting with processing power and storage capacity, they seem set to become a popular device in many embedded applications. There's been a lot of hobbyist interest, too, since the devices look like a painless way to add intelligence to electronic devices.
This is a Wiki. The idea of a "Wiki" site is that anybody can contribute to pages to add their input. Surprisingly, they tend not to degenerate into chaos; especially not when the Wiki mainly exists to serve a niche, like this one.
See http://www.usemod.com/cgi-bin/wiki.pl?WhatIsaWiki for further background information.
If you have links or information to add, create yourself a user (by clicking Preferences above and setting yourself up, later you can [login here], remember your user ID!) and start editing. If you're not familiar with Wikis, then see [TextFormattingRules] and try playing in the Sandbox.
There are architecture versions and families, both of which are numbered, but which don't correspond 1:1. [Wikipedia's ARM architecture article] has a detailed chart. ARM7 chips are mostly v3, v4, or sometimes v5 architectures. ARM9 chips are mostly v4 or v5. ARM11 chips are mostly v6, and Cortex chips are mostly v7.
Some chips support alternate instruction sets for specialized tasks, such as Thumb mode and Thumb2 mode (for more compact code at the expense of speed), and Jazelle (for more efficient implementation of Java virtual machines).
http://www.interfacebus.com/Bus_Design_Top.html has lots of information on busses. http://www.ghielectronics.com/ sell an LPC2114 pre-programmed with an implementation of the FAT filesystem, and device drivers for IDE, MMC Card, SD Card, and Compact Flash, that your master device controls via RS232 or SPI.