Trans Union offers free locking..easily turned off and on, no pin via their TrueIdentity. You can also freeze your Trans Union report. There is a fee involved and pin, not quite sure of the difference, but they appear to have the same result.
Equifax was free for me yesterday. Experian wanted $10. I believe that varies by state.

Edit- locking through Trueidentity won't help much..from website:

About this feature:
-Creditors, lenders (when you apply for a loan), landlords and employers can request and view your credit report.
-Locking your TransUnion Credit Report blocks others from looking at it, which may serve as a critical step in preventing an identity thief from applying for credit in your name.

Who are the "others" that are blocked from seeing your report if creditors and lenders are not?
edit again...or maybe I'm reading the above wrong