There is a nice book of varied guitar exercises by a guy called David Mead with three sections - Warm up, coodination and ear training. The idea being to do 2 minutes on each exercise, one from each section, once a day. Having chosen the exercises at random to avoid boredom.

Each has three speeds - beginner, medium, advanced. So a beginner may do something between 2 and 15 times in 2 minutes, an expert 40 times.

Only £5 and available from his site or bookshops. Fits in your pocket as well. Some more details at Basic Guitar Workout