Try using http://www.kayak.co.uk
It’s a price comparison web site, which searches multiple airlines and consolidators. Very useful for quickly searching fares across the market. I have also found it useful for finding routings I would not have thought possible myself.
After entering the initial search criteria, wait for results to appear. Then you can use the very comprehensive filter options shown the right hand side of the screen to narrow down the results. Including searching just particular airlines or airlines within the main alliances.
A sample search for LHR to SIN in business class for May 2010 out on Saturday 22nd May and returning Saturday 29th May searched 32 different travel providers. Cheapest results were for Turkish Airlines at £1679.
I have no direct or indirect affiliation with http://www.kayak.co.uk what so ever. I am just a user who has found it useful for some of my travel planning needs.