I'm pressed for time in the morning (who isnt? ) and can only spend 30 minutes at the gym doing a weight workout after my cardio. What machine's should I use to hit all the major muscle groups?

Deadlifts and Bent Presses would be very good choices and are my preferred choices most of the time. They may take a little time to learn proper technique, but they will serve you well in the long run. To substitute bent presses in the beginning, you can start with military presses and maybe do some barbell/dumbbell bench press.

I would do these in an alternating fashion using heavier weight and fewer reps. Learn the proper technique before moving to the heavier weights though. At first, take as much time as you need before starting your second set, but do these for the entire 30 minutes. Work up to decreasing your time between sets so that you complete more sets in your allotted time period.

I know you are probably thinking this sounds weird, but it's not new and has been used by many peole over the last 100 years to build some nice physiques and strong ones as well.

deadlifts cover all your pull muscles
bent presses cover your push muscles

Every few weeks switch to an alternate routine for a couple of weeks then go back.

Another thing I enjoy doing is training PTP (Power to the People) style because it allows me to complete a workout well within 30 minutes. The basics of it are 2 sets of 5 for two exercises (deadlifts and bent presses) 4-5 times per week. Increasing by 5 lbs. every workout.

Aside from these, there are plenty of other options for you to use.