Things I would say would be: (in addition to the op)

• Animated GIFs (any if not lots)
• Massive Images (as in 100's of kb in size)
• Thumbnails (like fake where it is the full image just specified at a smaller size*)
• Background images that make text hard to read
• Bad colour usage (dark on dark or light on light etc)
• Non-resizeable text

Can't think of any others atm... :P

* Just say an 800x600px image shrunk down to 200x150px instead of being recreated at that size (if you get what I mean)