Wiistar YPBPR to HDMI

-USB powered
-£16/$20
Good picture but unfortunately has black crush. Didn't test with the problematic Wii signal to check sync.
Mayflash comparison, you can see detail being lost:

Mayflash VGA box

-USB powered
-£11/$14 (Ebay)
Good picture, no chroma shift and shows the correct range with no black crush and is comparable to the quality of the more expensive GARO but can't handle the Wii's signal like the GARO (Bright white flashes cause desyncs e.g. Lighting in Double Dash). Works flawlessly with the Xbox. I did test with ps2 but can't remember if it held sync (Will update when I do).
Mayflash Wii/PS3 VGA cable

-Powered by the console
-£16/$20
Picture quality is as good as the Mayflash VGA box but it's even worse at holding sync, going into and out of channels on the Wii dashboard will cause a desync. Didn't test with a PS3.
Portta HDMI converter

-Mains powered
-£14/$17
Good picture with the best brightness I've seen from these converters, unfortunately, it shows black crush in my tests and a few amazon reviews mention a darker picture also. I saw some infrequent intermittent drops, this could be a psu issue.
Keydigital KD-CTCA2

-Mains powered
-approx £21/$26 (out of print/ebay import price)
I saw a lot of chroma shift on this and the image seemed a little too saturated, it broke quickly after purchasing.

HD Anywhere video converter

-Mains powered
-£8/$11
Awful picture quality with chroma shift and off looking colours.
UNTESTED
Neet - Component to HDMI

A couple of reviews mention a darker picture so my guess is these are crushing black, there's a few user pics on amazon that look like they're exhibiting crush but can't say for sure.
I'll update if I try some other models. Hope this helps and if anyone has any impressions of other models feel free to post them!