I came across this one today - a 5 day mtb race in Timor, August 24th to 28th, 2009.

It's a really interesting concept, free entry (to support tourism), a big prize pool, and several possibilities for sponsorship. It's a mix of bitumen, variable quality dirt roads and river crossings, with plenty of hills and spectacular landscape thrown in! Have a look at the course http://www.tourdetimor.com/Race-Route.php then think about what bike you'd want to take.... cyclocross, hardtail 29er with narrow tyres etc.