Most bullet proof iPad case?

Has anyone got any suggestions for a seriously strong iPad case? I'll be cycling about with it daily and have been known to take a spill or two. Also it would be good if it had closeable access ports as I work around a lot of sawdust on a regular basis. Any ideas?
Cheers.

I think the Otterbox Defender is the most heavy duty case:
http://www.otterbox.com/defender-series/defender-series,default,pg.html

They also make a lighter one, the Commuter, which may be enough for you:
http://www.otterbox.com/commuter-series/commuter-series,default,pg.html

31trum products make some very good cases
search the forum for 31trum

Also heard good stuff about the Griffin Survivor Amazon.com: Griffin Survivor Case iPhone 4/4S BLACK: Cell Phones & Accessories

Survivor. Our strongest iPhone and iPod touch case. - YouTube

I just realised you asked for iPad cases and not iPhone… it seems Otterbox also do cases for iPad so might still be worth checking out: http://www.otterbox.com/apple-ipad-cases/apple-ipad-cases,default,sc.html

I have a Griffin and it is very, very tough. I dropped it down stairs at work when my Barack pack strap parted and after bouncing down 10 concrete steps the case was practically unmarked and the ipad worked fine, and still does.

Another vote for the Griffin, it's bombproof and seems well sealed against water when all the rubber tabs are sealed up.

the g force one is pretty impressive:
iPad Survives 100,000+ Foot Fall From Space Near Area 51 (High-Res) - YouTube

Thanks everyone. I think I'm leaning towards the otter box.

Check out the products from Tech21. They all have D3O in them (military grade impact stuff). I have a iPhone and iPad case from them and its great. The leather folio case looks the business too without looking to "safety" like the otterbox.