I know this has been covered several times on this or other forums but...
I was all set to go about making or buying a tool to align my enlarger (I have never done this and couldn't seem to ever make it come out right with a negative with pronounced grain in the holder). About a year ago I purchased a laser level at Lowe's--on special for about $49.00--to put in a paver patio in my back yard. The unit has a spinning head to project a horizontal line as well as a vertical beam. I simply leveled the device as you would if it was on its tripod and used the vertical laser to shoot a beam up at a mirror on the neg stage as well as the lens holder and centered the dot. Worked like a charm! Not to mention the unit has about a billion other uses around the house! Before you spend any money on a dedicated laser alignment tool-check out a laser level at you local hardware store.