Man, im right now the same situation as you, optus crap 3 gig plan.. Just signed up to TPG 3 days ago. will be going on the ADSL 256 unlimited plan for $69 a month. They have a special deal going on that if you signup with them within these few weeks, they are throwing in an ADSL USB Modem for free!!!
Been searching around for other ADSL ISP's but seems like TPG is the way to go with the special deal going on and probably one who you can trust as well.
Anyway Inasnt, saw your car @ Glen Waverley on Saturday night.. NNNiiicceeee Indeeddd....
On another note since you are with optus, is your home telephone line with them as well???? If you are then you CAN'T get ADSL since they use fibreoptic cables rather than copper.
In that case you will need to signup to another home phone line with Telstra as only Telstra uses copper.
If you are in doubt, goto: www.whirlpool.net.au they have all the ISP's listed in Australia and can use their search function to find the best and cheapest plan for you own need.