I think Alistar top counters Singed very well. All he has to do is heal his minions when the poison gets them low. This is gonna waste Singed's mana early game and make Singed commit to pushing the lane hard. Once he's pushed in he headbutts Singed into the turret, then pulverizes. It might not kill him but it harasses him enough to keep him low for a gank top. Alistar's ultimate keeps him pretty safe from turret dives from Singed on the gank too, which we all know he thrives on.

Thoughts? Comments? Criticisms?

Or counter with udyr or ww

I think it works but not necessarily for the reason you are suggesting.

I think not chasing singed is all the counter you need.

I think it has more to do with Alistar being able to outposition Singed more or less regardless of creeps.
Simply put, Alistar can stack damage on Singed without fear of retaliation.

But Darkjuggalo is right as well -- it would be a unique comp to value Alistar top over Warwick or Udyr.

ranged AD is singeds kryptonite early game... just put a teemo top and deny him all day long

AD Sion or Gangplank top just run at him and autoattack him down from lvl 1 singed has no sustain and no real damage lvl 1 so its pretty much instawin you will either force him to back or get free kills and deny him hard either way
eg with a gp top vs singed i managed to get 6 kills on him in 15 mins (including under turret and jungler assisted) and he had like 40 cs by that point singed does not win 1v1s in almost anymatchup

oh and AD Sion just get either ur stun lvl 1 and go for him straight away or get ur e and farm if he comes anywhere near the creep wave get free hits on him with your much higher AD then when you get ur stun and shield it just gets worse for him