The newer slim version also has the benefit of WiFi. For the older models you have to buy an adaptor for £59 .... or cheaper if you shop around.
The new controller (kinect) will work with both machines but with slim version it doesn't need a separate power supply as it uses the connection with the xbox to run.
im a playstation 3 person but what i do know is:
there is the very new xbox called the kinect, dont know much about that but i know its a little like the wii. sounds brilliant tbh. or there are the older models, think there are 3 of them? the arcade, the something else or the elite.
here is a link i found, this guy explains it all quite clearly: