I used to collect soccer jerseys as a kid, so this is a great question for me.
I really love some of the cool designs that sports teams wear these days, and I have always been a fan of "unusual" kit designs - ones that break the mould.
Of course, as a soccer fan, I'll always be biased to the teams I support. I grew up supporting Milan (AC Milan for those of you not familiar with Serie A), and since I moved to London for university, I've also been a big Arsenal supporter.
Here are my favorite Arsenal and Milan kits:


Other cool football jerseys
As I mentioned above, I really like kit designs that you wouldn't normally see.
The bright yellow of Borussia Dortmund is a great example, and when I play FIFA on the Xbox I frequently play with teams from lesser-known leagues because they seem to have the coolest kits!