Widest tire on a 23c rim? Alright, I've seen this question around the web a bunch but the other questions are always including limitations and restrictions by brakes or fork/frame capabilities... So my question is, what is the widest tire you could put on a 23c road bike rim, leaving out frame/fork and or brakes limitations. 

I ask this because I am looking for cyclocross tires for my fixed gear for some snow riding and I have a Surly Steamroller which has (what seems like) an endless amount of room for wide tires, but I can't find an answer on how wide I can actually go. I'm not planning on going oversized, mainly I'm wondering if a 33-35 would fit on a 23.

Also any recommendations on good tires for winter would be great! Thanks
See for a definitive (imho conservative) answer the almighty Sheldon Brown(bottom of page). The rim width can vary a little between wheels.

Having said that, I have been running 700-35c Cyclocross knobby tires on standard Shimano Ultegra road racing wheels for years without any issue.

Another really good tire for commuting and light offroading (gravel) to get on a CX bike is the Schwalbe Delta Cruiser (be sure to get the 700x28c version). Almost as fast as road tire, much higher comfort, long lasting and decent puncture protection.