I have had this clunk for a long time - it started at 15,000 miles about two years ago and I can assure you it is none of the reasons mentioned and its still doining it. Mine tends to be on the drivers side of the car and I have felt it through the streering wheel while reversing off the driveway. The car has been checked by the dealer twice and they cant find it. I have had the car in pieces trying to find out what this is, including;

Adjusting wheel bearings.
Changing streering damper
Checking steering box and linkages
Checking front damper and springs
Checking top and bottom swivel joints
Checking track rod ends
Checking for brake pad movement in caliper
Checking for loose rotors or calipers

I am left with 3 more posibilities;
The streering colum may be loose.
There is a joint in the steering colum which has a collar to tighten it - it this loose? its very difficult to get at.
Is the front suspenion leg creaking in its cup at the top and needs some grease in there?

When I get time Ill carry on looking!!