I started with a search at Newegg Australia. These are not bad.
http
/www.newegg.com/global/au/Product/Product.aspx?Item=N82E16836116044&cm_re=speaker-_-36-116-044-_-Product
A great set of 2.0 Creatives that will sound way better than the Logitech Z906. I've used them and for the price the Creatives are decent and can't be touched. They arn't surround sound however, so if that's what your looking for then look elsewhere. Personally for music, games, and even movies I'd take the creatives over the logitechs. Much better sound reproduction.
Now if you want to step it up a notch and get into real audio check out the following from Musos Corner in Australia. You should be familiar with that store. These will kick but at a decent price range.
http
/www.musoscorner.com.au/eris-e4-5-2-way-4-5-studio-monitor-pair
The preSonus monitors are 50W each compared to 16W with the Creatives. They have balanced XLR inputs which you're probably not use. The second speaker connects with plain old speaker wire so you can easily make it as long as you want. They also have an auxilary input and headphone output. I check the reviews of the PreSonus monitors and people claim they are good enough to be used for studio mixes. For under $300 this is probably the best you'll do.
If you want surround sound I'd hold off for a real home theatre. But for music and gaming these monitors will even outshine a surround sound home theatre.
I have been assuming your going to use these with a computer. I may be wrong.