A 3 Barracks opening that I like to use. Build order is posted below. Numbers represent your supply at which you make that unit/building. Numbers assume no units lost. Numbers may be slightly off, just worry about doing them in order as quickly as possible.
10 Supply Depot
14 Supply Depot (Finish Wall-in... every map is different)
17 Orbital Command
17 Tech Lab (First Barracks)
17 Supply Depot
18 2nd Barracks
20 3rd Barracks
20 Supply Depot
24 Reactor on 2nd Barracks
26 Supply Depot
MAKE SUPPLY DEPOTS NONSTOP WITH 1 SCV
27 Tech Lab on 3rd Barracks
CONSTANTLY MAKE 2X MARINES AND 2X MARAUDERS FROM ALL BARRACKS.
35 2nd Refinery
PUSH OUT ONCE FIRST MARAUDER SPAWNS FROM 3RD BARRACKS
Constantly produce units.
Depending on how our attack goes:
Goes Well: Keep pressure up, producing units
If Goes Normal: Tech to Medvacs
If Goes Poorly: Turtle and build Command Center in main to expand.