Many of you already know about PCSX2 but I thought I'd share this to those who don't...
From
PCSX2 Wikepedia entry
PCSX2 is a PlayStation 2 emulator for the Linux and Windows operating systems. The emulator has been improved greatly since its first release, though it is still in beta as of July 2006. As of July 2006 and version 0.91, many PS2 games are playable (though speed limitations have made play-to-completion tests impractical), and a few have full functionality. The main bottleneck in PS2 emulation is emulating the multi-core PS2 on PC architecture. Although each CPU can be emulated perfectly, getting the synchronization and timing between them to be accurate is difficult.
PCSX2, like its predecessor project PCSX, is based on a plugin architecture, separating several functions from the core emulator. These are graphics, controls, CD/DVD drive, USB, sound and Firewire (iLink) ports. Different plugins may produce different results with one game, in both compatibility and performance.
Performance before 2006 was between 2 to 15 FPS (frames per second) depending on the game, PC hardware, and plugin configuration, with the PS2 BIOS itself being one of the fastest pieces of software to emulate. Since release 0.9 in April 2006, performance has greatly increased. Most 2D games and menus can reach 60-120 FPS, though ingame 3D is still slow in many cases. In this release, PCSX2 also began supporting dual core CPUs, resulting in an effective doubling of FPS on systems with dual core processors. As of July 2006, the fastest dual-core CPUs can run popular 3D games, such as Final Fantasy X, at over 60 frames per second. PCSX2 is under active development.
As of August 31, 2006 the PCSX2 compatibility stats read:

- 120 - Nothing

- 224 - Intro

- 116 - Menu

- 410 - Ingame

- 285 - Playable
Keys:

Playable
You can get from 'new game' to 'end credits'. This is regardless of FPS, it simply means you could with a great deal of patience, complete the game! eg: Slow, but stable!

Ingame
You can get through menus, intro cutscenes / videos, and see ingame graphics, but either due to graphical bugs, crashes, un-resolved errors, you can't play through the entire game.

Menus
You can get into the menus, be it past 3D / video intro, memcard checks etc, but when starting a new game, it will lock up, crash, enter a loop etc.

Intro
The game will show 2D logos, or video, but will not get into menus. This could be one screen, or 20, but won't show much.

Nothing
Exactly what it says, this game crashes before showing any graphics, making any sound etc!
Though they're very far from having 75% of the current PS2 games from being playable, the number of current playable games is promising :mrgreen:
But for those who have low- (to even mid-) range computer specs, you might find yourself disappointed when you try to play the games listed as playable. Reason? You're system isn't up to the job.