Many others have mentioned "Whirlpool". It is a good resource for all things DSL. Here's a link to their plan search and FAQs on choosing a provider:
http://whirlpool.net.au/wiki/?tag=Ch...Provider%20FAQ
http://bc.whirlpool.net.au/bc/?action=search
There is an absolute plethora of providers out there now. There are many plans without 12 months contracts. Your first foray into DSL is sometimes the most difficult so go for a "named company" like: TPG, Internode; iinet; Netspace. Stay away from Bigpond!
Look for a plan that has plenty of download limit. I cannot guess your requirements but don't get a plan that has exorbitant excess usage charges...like Bigpond does. If you read their forum you'll find plenty of posts with monthly excess bill of $k of dollars. So keep away from plans with high excess usage.
A better bet is a plan that "Shapes" your excess usage. That is slows your connection speed if you go over your limits but does not charge you extra.
A good 1st time provider is Internode or TPG. The have good help desk support. Try for at least a 512K plan or faster…256K is too slow.
Lastly look for a provider that has ADSL2+ infrastructure in your local area exchange. Many of these ADSL2+ plans are cheaper than ADSL1 as they do not have to pay use Telstra's line charges and the bonus is you get much faster speeds.
http://bc.whirlpool.net.au/bc/?action=list
Good Luck.
Edit:
I forgot to mention many providers have bundled plans. That is you bundle you internet plan with their telephone service. This is something that I avoid..it's a personal choice.
edit edit:
We use on average 8Gb to 10 Gb a month plus with a family of 3 kids.