Mothers Direct (ABA) Cool Sling
This is fantastic as an alternative to a pram whilst you're shopping and a lot easier on your back when getting out of the car!
It's very quick to assemble and keeps my hot little bubba at a good temperature.
The only thing I don't like about it is that it doesn't appear to be particularly comfortable for bub when I sit down. I think this is a fault particular to lots of 'upright' type slings, though.