I had a squeak or two on my Specialized Allez a1 and was about to post a question, probably asking something pretty vague and non-specific. At the last moment i decided to do a search on the forum - wow! With specific tips and links to various sites I now have the most silent bike I've ever had!
The real learning point was that a squeak / creak / rattle is not always related to where you think. I thought my headset was squeaking - turned out that the plastic nipple(?) which feeds the cable into the guides on the downtube was the culprit! Also, what I thought was a creaky crank / pedal was solved by tightening the front quick release skewer. Thanks to everyone who posted these gems in the past.