In terminal C, you need to go to gate 17 or 18 on the north side of the airport to get the best view of the lineup at D.
British Airways is now using 777s for their daily flight to LGW. Their second flight still runs several days a week (I'm not sure which days) and it is also a 777. The switch from a 747 to 777 is a recent change.
Air France and Lufthansa are both still using A340-300s on their flights. As B757300 said, you will also see KLM and you may see TACA, Aviacsa, Aeromexico, Cayman Airways, Air Canada, Alegro, Air Jamaica, and others that haven't come to mind. World Airways runs a regular charter MD11 to Angola. Often it is sitting on the hard stand by terminal D.
As for CO, there is only one 767-400 a day and it departs mid-morning for HNL (usually gate 14). The afternoon flights to and from Europe, as well as NRT and a few EWR flights are operated by 777s. There is usually at least one sitting around somewhere (if you're lucky, you will see the Peter Max plane, but its usually operating out of EWR). The 767-200s also come and go through out the day. Most of those are domestic flights out of terminal C.
There is almost always an AN-124 or two sitting around, but they usually are not in view of the terminals. Have fun!