Most people would say Tough.pro but I'd go for iSEO.pro. I know it's short and SEO is big business but I don't think .pro is strong enough to support e's and i's in front of generic keywords. Value falls off a cliff when you start doing that.
For example, I heard the owner of Debt.com was open to offers in the $1m-$2m range a couple of years ago. The owner of eDebt.com told me he turned down an offer of $30,000 in 2006. eDebt.mobi sold for $95 in Feb 07.
Worst case scenario you might be looking at $50-$100 for iSEO.pro when there are niche generic .pro keywords still unregged that could sell for $XXXX+ to the right industry buyer. If you are regging iSEO.pro for your own use that doesn't matter, I picked up domains like Mango.pro and Indigo.pro purely for "ring to it" own use with web design in mind.
However, with something like Patient.pro I'm covering both development and resale angles. I wouldn't be able to sell it wholesale because it's not a domaining keyword but it could be worth alot of money to a healthcare company. The owner of Patient.org wants $400,000 for it and in my mind the .pro sounds alot more commercial and profit oriented.
I think Dairy.pro is a similar industry keyword that you wouldn't be able to sell to another domainer but could be worth alot of money to the right buyer and the $12,500 sale of the .co.uk proves that.
I audited a company that toughened or "ruggedised" laptops for outdoor use. It's a big business, not just with laptops but with any professional equipment used in harsh environments. I think Tough.pro would be a brilliant name for a company working in this industry but you'd have to direct market it to them.
Accessory.pro is probably the strongest name in the list. Not an obvious domaining keyword but a logical fit and flexible. I regged Uniform.pro in 07 for similar reasons. I like Stay.pro, very short, flexible, and brandable. I regged Switch.pro and Move.pro along similar lines last year.
