i'm very happy with the tucano second skin sleeves, i used one with my ibook and i've bought one for my macbook, for transportation i put the mac in the sleeve and then in a simple laptop backpack from case logic
I use the black foamy incase sleeve for my 17". They make it for the 15 and 13 inchers as well. (It's bright green on the inside). The material gives good protection for being a sleeve.
Although I'm still shopping around for a carrying bag; right now I use a swiss army backpack.