Here is Thorzain's famous 3 rax fast expand build. I wanted to test this out so that I could move up in leagues, so I played Very Hard Terran, Protoss, and Zerg and it worked against them all. Is FAR less likely to work against INSANE AI. Here's the build order (sorry about the audio quality in the video, my mic has been auto adjusting):
10 - Supply Depot
12 - Barracks
15 - Upgrade to Orbital Command
15 - Pump out marines 1 by 1 and add a supply depot to block off
17 - Drop down second Command Center as soon as you drop a MULE and start an SCV
17 - Keep pumping out marines, NEVER stop.
19 - Refinery with 2 workers
23 - Drop down TWO more barracks (pull an scv to do this)
27 - Upgrade second CC to Orbital Command
27 - Start your tech lab, and upgrade to combat shields ASAP
30 - Drop a supply depot and another refinery with 2 workers
38 - Reactors on barracks 2 and 3. Drop a supply depot (and keep up with supply as necessary)
At this point pump out marines non stop, and scvs to your two expansions (move over 2nd orbital when you feel ready)
38+ - As soon as you have 100 gas, drop a factory then stim packs, then startport. As soon as starport begins, start reactor on factory and swap it with startport. Pump out Marines and Medivacs at this point.
Down the line, IF NECESSARY AND RESOURCES ARE AVAILABLE, put down a couple engineering bays and get upgrades.
As seen on TEAMLIQUID TERRAN WIKI