Powerlifting will give you great strength and power without putting on alot of weight/size.
At the moment I am doing no MMA, but if you do the following exercises once a week you should find you are making progress: -
1.) Chest - flat bench barbell
2.) Back - deadlift
3.) Shoulders - military press
4.) Legs - squat
5.) Arms - barbell/dumbell curl/whatever.
These in my mind hit the areas hardest/most overall.
Of course you could then split these down to 2/3 days a week - job done.