Bottom bracket creaking
Creaking from the BB area can be hard to localize, but there are basically 5 sources:


The cups holding the cartridge in place are a hair loose, and the cartridge is moving around a bit.  Not a real big deal but should be fixed.
The BB cartridge bearings are going bad somehow.  Unlikely.
A pedal is making noise.  Sometimes this is indicative of a bad bearing, sometimes it's just what the pedal does.
The pedal is loose where it's screwed into the crank arm.  Needs to be fixed fairly soon, or the crank arm can be damaged.
The crank arm is loose on the crank axle.  This is a serious problem and needs to be fixed right away (if not sooner) to prevent damage to the crank arm and the axle.