Build Orders

Basic Protoss Order
This is the standard beginning for most protoss build  orders, as it gives a good economy, and lets you make early units for defense or rushes, and lets you get anti-air in the form of dragoons fairly quickly.

7th probe: pylon
9th probe: gateway
12th probe: Gateway, pylon (at this point, warp in a zealot for rush protection)
14th probe: assimilator
15th probe: pylon

After this, the road pretty much forks depending upon what your strategy is. Usually, i will continue warping in gateways till i have somewhere between 4-6.
Also, remember to keep making probes, and STAY AHEAD ON PYLONS!! If you fall behind on pylons and hafta sit there and wait for the pylon so you can make units again, you will be screwed really easily and fall way behind compared to other players who managed to stay ahead on pylons.

Turtling Order (Don't do this if you can help it!!)
"Turtling" generally means favoring defense (cannons) over mobile offensive units (zealots, goons) early in the game.  This is accomplished by replacing gateway 1 in the build order with a forge, and then making cannons all over the place.  I only recommend doing this in FFA's or comp games, however.  Players who do this in allied mele games piss me off, and i make it a priority to kill them off ASAP.  Turtling is and awful strat if the other player(s) have offensive units, cause they can double team you, break through your feeble cannons, and you will have nothing to defend with, and die.  Most toss players turtle so they can make carriers, and then "break out" of their shell with the carriers in hopes of killing everyone in sight with them.  This only works against crappy players, or other turtlers who turtle slower than you do.  If you DO turtle as toss, planning on going carriers or reavers, make templar with psi storm so you can ward off flying enemies or masses of enemies.  However, even if you plan on doing this, good players will kill you 5-10 minutes into the game if they see that you are turtling - so be careful!!
7th probe pylon
9th probe forge
12th probe 2 cannons by nexus
13/14th probe make pylon at entrance, and begin warping in 7 or 8 cannnons when you have lotsa minerals stored up. 
Then....warp in gateway/cybercore/and whatever else that will lead to your main offensive strat (robo fac. for reavers, citadel for temps/archons, stargate for carriers/scouts)

Zealot Storm
After following the order listed above, warp in the citadel of adun and get 5 or so gateways and pump the zealots out like a madman.  These things are one of the best ground units in the game, and can rip apart a lightly-moderately defended base pretty fast.  I dont EVER advise going ALL zealots though, since they cant attack air units.  The  exception to this is if your teamate can support you with anti-air units.  Even then, though, you still need to cover your ass at your base.  When going for the zealot storm, you want to have killed your opponant within 10-15 minutes, cause that is plenty long enough for them to have built units that can kill zealots quiet easily (like carriers, tanks, mutalisks, templars, etc.).

Dragoon Storm
This strategy really kicks if you are fast enough and stay ahead on pylons.
Follow the Standard Toss build order up till the 15th probe and warp in the Cybernetics Core.  From there, keep making zealots for defense, and make a second assimilator.  Then, begin pumping Goons.  When you have 8 zealots and 6 goons, attack someone.  Goons and zealots make an AWESOME early attack force, and can rape both your enemies units and cannons.  The key is production.  When you send in your goons to attack, use the "A" key and left click on the back of the enemies base, so the goons will gradually work their way to the back of the base, while killing anything in their way.  While the goons fight, do NOT micromanage the attack, but return to your base and make MORE dragoons, and then send them.  As long as you are constantly sending reinforcements, the goons will destroy everything, and you will win: its that simple.  Again, you hafta do this withing 15 minutes, before the enemy has too much defense or else you may be in for a spanking.  This strategy was my mainstay during my "glory days" on battlenet.....just keep at it and soon you will become a machine of invincibility vs. most players out there.

Reaver Drop

There are basically two different reaver drops: the quicker, risky one, and the delayed, but much more powerful one. 

Quick Reavers:

For quick reavers i use this build order:
7th probe pylon
9the probe gateway
10th probe assimilator
11th probe pylon
12th probe cyber core

From here, make another assimilator ASAP and make some zealots/goons for defense.  Warp in the Robotics facility when you have 200 minerals and 100 gas.  Make a support bay and another robo. fac. ASAP, and stay ahead on pylons.  For added Defense, move the reavers to the choke point behind your zealots and goons (like siege tanks are used).  When you have 2 reavers and a shuttle, load em up and drop em!  Caution:  YOU CANT MESS THIS ORDER UP, OR YOU WILL DIE!!!!  Never fall behind on pylons, or fall behind on probes, or you will DIE because they will attack you before you have any reavers to help you defend. 

Alternative/Delayed Reaver Drop:

Use either the General build order up to the 15th probe, or use the turtle method.  You dont hafta "rush" towards reavers like on the quick reavers order (although you should still build as fast as you possibly can!).  After you have a solid base of goons/zealots for defense, warp in 3-4 Robo Fac's and 2-3 support bays.  Dont forget to make at least 1 or 2 more assimilators too!..Also use observers to see if your enemies back door is open for a drop at this point in the game.  If, so, load up 4 shuttles with 2 reavers in each (or maybe some goons if your anticipating wraiths, scouts, or mutas waiting for you).  Then drop them off in his base and watch the wrath!  If you see any tanks in siege mode, unload the reavers RIGHT NEXT TO the tank, so it cant siege the reavers. 
If NO ONE's back door is open for your attack, you can either attack them at the front (choke point), or warp in some stargates and make scouts/carriers or more goons and zealots and THEN attack with your entire force.