Cog with the widest shoulder

Which brand/model of cog has the widest shoulder? I need a new one and this might just help my chainline issues a bit. Currently I have one of the miche w/carrier types and my chainline is 3 mm-ish out, it doesn't really do my head until the end of the day when I can feel the uneven contact feeding back. This has also been compounded by the fact I had a ride on a friends bike with much better chainline and it felt so much smoother and easier to pedal.

Would you consider the spacers that Velosolo do?

If you don't want to get a new bottom bracket or new hub, try an EAI - should give you an extra mm:
http://sheldonbrown.com/chainline.html

i used some old bottom bracket spacers i found in my box of bits and they do the job

a wider cshouldered cog might take up to much space and you can't really put spacers on the hub, you might not be able to get a lock nut on.
so best option would be a wider b/b.

Out of interest, what's the issue with a 1 or 2mm spacer between the hub and cog?

won't leave much room for the lockring

I was about to suggest spacing out your chainring, then I remembered you'd need negative spacers, almost as hard to get as negative shims. I'm always dodgy about using spacers on the cog and stuff, probably due to having cogs lossening and stuff over the years. What hub have you got, you could maybe re space that but then it will need re dished

Yeah I'm not too keen on putting spacers by the cog as it makes sense to me to have as much cog thread in contact with hub thread, and likewise for the lockring theads if that makes sense. I've already tried putting the chainring on the inside of the spider and it results in the same difference just the other way. The BB I'm using is a 103mm one and as far as I'm aware there aren't any narrower ones (and I'm a lazy fucker and can't really be bothered to change a BB) also the BB width issue confuses me slightly anyway as I've heard of 103mm and 107mm BBs giving the same chainline which makes no sense to me. Redishing is an option but I'd rather not as I do use the other side of the flip flop hub when it gets to the end of the week and I want to use a slightly easier gearing. The eai cog looks good as I've heard good things about them anyway and I'm not too impressed with how quickly the miche one has worn down.

maybe help us by telling us what hub, cog, bb, cranks, chainring you have at the moment

On-One hub
Sugino 103mm BB
Sugino Uno/RD2 cranks
Sugino Uno/Messenger Chainring
Miche quick change Cog