These are what I originally had,
http://www.ebay.co.uk/itm/XBOX-360-...G_Replacement_Parts_Tools&hash=item1e64945286
They are non-OEM and are complete and utter shit. Tension wise, they felt fantastic. Control wise though, while playing Fallout 3, imagine moving your character (and aiming) with dpads instead of analogue sticks. That is how bad they worked.
The one on the Ebay US website aren't listed anymore.
1)
http://www.ebay.co.uk/itm/Xbox-360-...G_Replacement_Parts_Tools&hash=item27c01e2292
Looks extremely similar, except the pots aren't numbered on the OEM ones (mine, at least, all the ones I've seen).
2)
http://www.ebay.co.uk/itm/Xbox-360-...G_Replacement_Parts_Tools&hash=item2ec2518fa6
Picture is that of the OEM ones, but I'm not sure if it's a stock picture or not... the description "They're third party parts, not Microsoft, so they're a good price. If you're wondering about build quality they're not quite as nice to look at as the official ones and may not last quite as long but they're solid enough and will do the job, plus I can do them at a great price." would make me extremely wary of them, but it's also a bit misleading. The OEM parts aren't Microsoft to begin with, but I think that's more of a technicality than the seller would get into. My guess is that it is in face a stock photo, the item is probably a little different.
3)
http://www.ebay.com/itm/2-3D-Analog...t=Video_Games_Accessories&hash=item41694823c8
Off of the US website, but he ships internationally. Pic is again of OEM ones, no description. I'd feel more confident about this one.
I'd be tempted to go with the third one, but if you decide to do some of your own snooping around, I just snapped a few pics to point you towards what to look for.
Stick is turquoise, as are the two pots. The middle click stick is white/offwhite, with a black button, button housing, and bottom plate. Plastic in the cage, not visible from any picture, is white, just like the middle click stick.
Pots are not numbered on the OEM ones. Nor are they this vibrant, thank the camera flash for that. They do have those red portions, but they're a bit more maroon colored.
Most importantly, ALPS branded. ALPS makes the OEM sticks in every controller I've seen so far.
I'll also say that I've yet to put these sticks in my controllers, but they are a 1:1 match to the ones I took out of them originally. Color of components, branding, everything is 100% identical between them, so if you're going to have luck with anything, it'll likely be these.