What are the stiffest alloy bars and stem out there for road riding, and are they always the same brand?
If you develop a smooth riding styler there is some question as to why you would need the stiffest possible bars and stems. It is hard to see how a little flex there would result in any performance loss.
you seem to be quite concerned w/ finding the stiffest bar & stem...any particular reason why you think you need them?
i work for some bike racers...
2013 Trek Madone 5.9 w/ '12 SRAM Red
2012 Trek Cronus Ultimate w/ SRAM Red Black
2010 Cervelo T1 sprint bike
2011 Cervelo P2 pursuit bike
FMF 24" cruiser
Bianchi Pista road fixed gear
1949 Columbia 26" cruiser w/ SRM & fenders...and rust
'05 Suzuki DRZ400SM
The Deda 35 series are claimed to be designed for extra stiffness. I have no personal experience since I'm not a sprinter and don't have massive upper body strength, so I choose flat 3T Ergonova bars for comfort.
As mentioned by skepticman, Deda's Trentacinque is very stiff due to a continuous 35mm top/clamp section. Another good choice would be PRO's Vibe series which has a straight 31.8mm top section (as opposed to tapering from 31.8 to roughly 25mm, which most other bars do). I'm not a fan of these because I don't like the huge top sections for grabbing during climbing.
Honestly, any quality alloy bar and stem should do the trick. I'm no lightweight (5'10" and 170 lbs), I'm a fairly good sprinter, and I use an FSA OS-99 stem and Energy T bars and I have no problems with front end stiffness. Unless you're a 220 lb gorilla doing tons of crits I wouldn't be too concerned with getting "the stiffest" bar and stem combo out there.
However, I agree with cxwrench, I would love to hear why you are looking for something so stiff.