Seeing Celtic_Growers 'The Art of Sowing' in Basics prompted me to post this. It is a simple strip of wood with cut-outs. After sieving the compost into the tray and tapping to settle it, I just draw the wood across to remove the surplus compost, give a smooth suface and provide a gap between the top of the tray and the compost.
(http://i12.photobucket.com/albums/a215/jennympics/Levellingstrip.jpg)
Nice tip jennym, I'll put it in the wiki
Think I might put one in my greenhouse too!