Good - Leaptel, Superloop
Good but expensive - Aussie Broadband, Launtel
Okay - TPG, Spintel
I avoid Telstra and Optus and most of the other providers, so can't comment on those.
Typically, I switch back and forth between Leaptel and Superloop as they normally have 6/12 month deals. One downside with Superloop is that you are expected to give 1 month notice when switching away. Sometimes you can get away with not, but I wouldn't rely on it.
I'll add that Exetel is owned by Superloop now, so experience will be roughly the same (but they use PPoE which is slightly annoying).