I'd never heard of this before but I've decided to put my name down this year:
http://www.greatbikeride.com.au/
It's a 10, 53 or 106km ride around the Swan River to raise funds for several worthwhile charities. 21/11/2010.
Some of the keen bike people on pwrx probably already know about it but I thought I'd mention it. I'm going to try the 53k ride (otherwise I'll need lights on the bike as I stumble home after dark.)