Here is the thread I promised. It will get more added as time goes. I've also included some known bugs and my experience with each as well as other interesting info in the "Notes". (List is Alphabetical by Manufacturer/System, please feel free to reply with info on new version alternates etc.. I will try add and rate each.)
Systems:
Atari 2600:
Name: PSP2600
Current Version: 1.1.4 (07/28/08)
Homepage:
ZX-81's PSP2600 Page
Download:
Download PSP2600 - CFW 4.X ,
Download PSP2600 - FW 1.5 (Add-on)
Rating: C9/S10
Status:Alive!
Notes: Pitfall II not playable, but all other ROMs tested playable at full speed. This emu is mature and still being updated.
Atari 5200:
Name: PSPAtari
Current Version: 1.1.3 (02/12/08)
Homepage:
ZX-81's PSPAtari Page
Download:
Download PSPAtari - CFW 3.X ,
Download PSPAtari - FW 1.5 (Add-on)
Rating: Not Tested
Status:Alive!
Atari 7800:
Name: PSP7800
Current Version: 1.1.3 (07/23/08)
Homepage:
ZX-81's PSP7800 Page
Download:
Download PSP7800 - CFW 4.X ,
Download PSP7800 - FW 1.5 (Add-on)
Rating: Not Tested
Status:Alive!
Nintendo GameBoy Advance:
Name: UnOfficial gpSP kai
Current Version: 3.3 test 2 build 132 (07/28/08)
Homepage:
Kimagure blog (Japanese),
Google Translation
Download:
UnOfficial gpSP kai 3.3 test 2 build 132
Rating: Not Tested
Notes: Requires GBA Bios file. (Not included don't ask) (Hint: Try Google)
Status:Alive!
Coleco:
Intellivision:
NeoGeo Pocket:
Nintendo/Famicom:
Nintendo 64: (Daedalus)
Nintendo DS: (Very, very slow....)
Nintendo Gameboy (GB/GBA/GBA):
Nintendo SNES/Super Famicom:
Nintendo VirtualBoy: (Yup, there is one)

Sega GameGear/Master System:
Sega Genesis/Mega Drive:
Sony Playstation (PSX): (Popstation, but will include more info and link to a FAQ I'm going to make for it.)
My rating system:
Compatibility:
1 Barely emulates anything
2 Executes some demos
3 Executes all demos
4 Executes demos and at least some homebrew
5 Executes at least one commercial (May not be fully Playable)
6 At least one commercial fully playable
7 A few fully playable
8 About half fully playable (Estimated based on personal/user tests)
9 3/4 or better fully playable (Estimated based on personal/user tests)
10 100% Playable
Speed: (Based on playable Commercial ROMs)(Need at least 5 compatibilty before it gets a speed rating)
1 Extremely slow (not playable) (AKA like <1 FPS)
2 About 10% speed (2-6 FPS depending on emulated system)
3 Slow >10% <20%
4 Almost playable >20% <33%
5 Slowly playable >33% <70%
6 Some near full speed (70%-90%) (This will be considered playable)
7 Some full speed with options turned down (AKA no sound etc...)
8 Most full speed with options on (AKA with Sound/Full Graphics etc...)
9 Most full with some able to go faster if options permit
10 All full speed some faster
Status: (Based on info from Official Sources)
Alive!

(Has seen an update in last 6 months or listed as alive by author)
Presumed Dead

(No updates in last 6 months and no updates on any of authors projects)
Dead

(No updates in over 1 year or listed as dead by author)
Yes, I realize not everything is here, but it's a work in progress.
Final note: If any links don't work or you wish to contribute or update this list please PM me.