We have a Littlelife Voyager S2 - being as I was pretty much just the donor of seed and now the person who watches our daughter so the wife can have a social life - I had/have very little say in things that concern the kid.
So needless to say it's the top of the line version and has everything with it - wee changing mat, stirrups, water/wind cover for small person (that also works as a pretty good sun cover as well). detachable rucsac and quite a bit of storage space in the carrier itself.
It is seriously comfy - with or without child - the top end one comes with all the extras but I'd recommend a Littlelife carrier to anyone.
Daughter is 2.5 years now and still uses it when we go for walks up the hills/countryside. I much prefer it to the pram (which now sits in the garage doing heehaw).
Can't recommend it enough...really good.
I suspect the main players are all very similar - some are free standing but watching youngsters wriggle around as they do, we went for one that wasn't free standing - it stands on it's own but won't stay upright without your foot in the anchor point (which we thought was good as it meant you couldn't leave the child, so there is no chance of the carrier falling over).
Think it should have cost about £180 but the good lady (wife for everything else - cleaning lady if she isn't within earshot!!!) got it for about £130 online. Link here and a review here (;-)).
Let me know if you want a nosey at it...we aren't that far away!