Where and how can I get the best international airfare deal ?

I want two tickets for a trip from Springfield MO (sgf) to Johannesburg, South Africa (jnb) travelling on or around June 25 and coming back on August 10.

So far the best deal is with Delta ($2750 all taxes incl.for us both) But I am sure we can get it for much better than that so now my question is where else can I look are there any really good travel agents or websites?Thanks for any advise.Where and how can I get the best international airfare deal ?
Delta shows 1336 each leaving 6-24 and returning 8-11



Thats a small savings