The whole work /holiday visa system changes alot, apparently canadians are allowed in until 35 for some countries. Some companies still offer the Uk upto 35 for oz as well but I have never found anyone who has actually been able to get in. I did find a few people who were in new zealand this year with the bunac visa and the only downside is that you have to pay them for their basic package to get it, which gives you support in getting jobs and accomodation.
Bunac come highly recommended as they were one of the first ever companies to organise work/holiday visas for universities and have been doing it for 57 years now. Also alot of people on the thorntree lonley planet guide forums and some of my friends have used them in the past and said good things.
One thing I have come accross in the last 4 years of looking at visas/volunteer type companies is that if the visa is available direct from the country there is very little point in paying a company hundreds of pounds to do the work for you unless it is a complicated visa like multi entry russia/china ones or a special international exchange one like the new zealand one. As all you are really doing is getting someone to check the forms you fill out and stick a stamp on them, and then send the final result back to you. They do not get any special treatment when it comes to processing them.
The volunteer companies are even worse they charge 600 quid and upwards for something that gives the organisations you will be working for the same amount of money as if you contacted them direct[for lodgings,meals ect], you still have to get there yourself and I fail to see how the experience is going to be so much better using a company as you will be doing the same work, living in the same accomodation and working with the same people.