There are plenty of choices, and Bill gives excellent advice - determine your environmental needs and then go shopping. In a mild climate, you can use an uncooled/unheated enclosure. More severe environments need more specialized enclosures. A number of these cameras have an available enclosure option from the manufacturer, but there are plenty of third-party enclosures as well.
The smaller cameras such as the Canon VB-C50i lends themselves to small "dome" enclosures, and are available with powerful zoom ranges.
It sounds like you may be glossing-over a more important issue... how are you going to distribute the video? Have you chosen server software or a service?
Keep in mind that if you simply use the camera's internal web server, you will potentially have multiple users accessing the camera over your Internet connection to the camera location, and you can very quickly overwhelm your connection. (Probably no more than 2-3 users, and even then performance may be poor.)
The solution is to send a single stream to a server and have the server redistribute copies of the stream.
If you expect multiple simultaneous users, this is your top consideration. Pick the server software, find out what cameras are compatible, and THEN go shopping.
You will also have to decide what streaming technology to use. I think today the emerging trend is going to be toward Flash video. Unfortunately, there are precious few choices at this point, they can be expensive, and they do require a PC at the camera site for encoding. (Or at least between the camera and the server.)
More end-users now have Flash installed than have Java installed. Flash video is also a lot more bandwidth-efficient than the motion JPEG typically used in other solutions (and typically supported by the camera itself.)