Try high intensity circuit training.
A set of weights followed by a 30-40 sec run on the treadmill (set treadmiil before starting and leave running) and straight back into another set of weights. This can be difficult in a gym so you may have to go at quiet times.
Alternatively just do a weights circuit with little or no rest between opposing sets.
It's hard work but gives you a good blast in a short space of time.
Intensity is often overlooked in training but huge gains can be made with this type of training.