If you ride in muddy conditions this might happen even faster
Its fairly easy to stop the creak with about 45 minutes of work.
Step 1: Tools
For Isis/Splined Cranks
10mm allen key
Bottom Bracket Tool Park BBT-24
For Square Taper Cranks
8mm Allen Key or 14mm Socket
Bottom Bracket Tool
For Outboard Bearing Cranks
10mm Allen Key
5mm Allen Key
Park BBT-19Park BBT-19
Cleaner, I user OranJ Peels and Bio Cleaner
Grease or Anti Seize
You should also have a torque wrench, I used the Park TW-2
Step 2: Remove the Cranks
On most modern cranks they'll have dustcaps on them that when loosening the crank bolt will pull the crank off. Side note, syncros sold these as crank-o-matics back in the 90s, then shimano came out with them...
Back on track, if you have square taper cranks or no crank-o-matics you might have to use a crank puller. You would thread that in and then turn the handle to back it out.
Step 3: Bottom Bracket
The drive side bottom bracket is reverse threaded, so lefty-tighty righty-loosey.
Step 4: Clean Out the BB Shell
You might want to use a small brush too if its really messy.
Step 5: Clean the BB
I went over it with a brush to get at all the crud in the threads.
Step 6: Clean the Cranks
Step 7: More Cleaning
Step 8: Grease
I no longer use plain old grease on bottom brackets and cranks, I use anti seize compound.
Step 9: Grease the Bottom Bracket
This is a debate as old as bottom brackets themselves, but I do not like to grease the spindle or the cranks on square taper bottom brackets.
Step 10: Tighten the Bottom Bracket
I used a torque wrench to tighten the bottom bracket to 300 inch pounds.
Park tools supplies a nice guide for torque values here.