Starting Strength can be done in about 30 minutes.
I read this in a Men's Health magazine and it has worked wonders for me.
On a treadmill, walk at a fast (not too fast, but fast enough to sweat) for 4 minutes, then jog at an incline for 2 minutes, then at the same speed but no incline for 2 minutes. Repeat. Do this for 30 minutes.
It depends on how hard you want to push it really?
Do you want to just bimble along for 30mins not really working too hard or do you want to go balls out for 30mins and be drenched in sweat?
I recently started couch to 5k which is a great program for beginner runners or runners that are a little rusty, like me. It maps out everything too!
Other than that, I like to utilize the cardio machines when I don't have a lot of time or I'm in a hurry and just do the bike or elliptical for 30 minutes.
Does your gym offer classes? Classes are also a great way to burn calories for 30-45 minutes.
Hope this helps! good luck and welcome! :)
I can't believe nobody's suggested New Rules of Lifting yet.
There's a ton of free ones on youtube like bodyrock or POP pilates or some form of HIIT. Also you can find free endurance programs like for running as an example.
New Rules can't be done properly in 30 min, a lot of the workouts take 1-1.5 hrs.
Something on this order maybe?