Dockjock
there are a lot of such sites. but I will tell you - they not doing the business in reality. they are a kind of Caledonian Wings - a lot of words and big homepages but almost nothing in real. I can bet that all together they doing less business per several month than just one of big CFA offices (like LON or FRA) per day. and there are no serious carriers presented on these sites - usually limited to airtaxi companies who can carry 50-200 kgs box.
internet is good and useful... for tickets reservation... but not for cargo charters.