The Fug by Crumpler is one of the best neoprene sleeves I've tried for the iPad hands down. It's a really slim and simple neoprene sleeve that tightly hugs the iPad all around. The Fug feels and looks really good, almost like it's the perfect slim sleeve made for the iPad. The stitching on the Fug sleeve are very well made while the top opening remains opened and zipper-less. Having a zipper-less sleeve is an advantage which eliminates the risk of your iPad's aluminum bezel getting scratched by it. Also, having the top opening allows you to quickly slip and slide your iPad in and out of the Fug sleeve.
I was a bit scared at first that the iPad will fall out due to the opened top, but the Fug actually secures the iPad tightly inside so it will not fall out even if hold the Fug sleeve upside down. Just in case, I don't recommend going about your day with the Fug sleeve upside down but you get the idea. The Fug's neoprene is slim yet padded enough to provides a decent amount of protection from various objects that could scratch and dent your iPad.
You can use your iPad with the Crumpler Fug sleeve even if you have various sorts of skins on the back as well as screen protectors. The Fug is really intended to be used with a naked iPad plus any skins you might have on, so you will not be able to fit any other slim cases inside. At the retail price of $40, I think the Fug is a bit overpriced for what it is. The quality is certainly there, though the price is the only flaw here. I would highly recommend the Fug sleeve if you can find it at a lower price. You can only get the Fug in red or black which is disappointing. I would love to see much more color selections from Crumpler. Price $40.