I love my Sigg bottles and never use the plastic anymore. They have a new sports top for the bike bottles that you can order from their site also. It has a flip up cover so it stays clean. You can twist and lock it or leave it open To drink you just push your mouth down on it and the flow is good unlike with the old tops you had to suck on. I put a neoprene cover on mine to mimimize scatching from the cages and it also keeps the water much colder for longer than plastic in my opinion.
http://www.mysigg.com/index.asp?Page...ROD&ProdID=353