A friend of mine is currently in Sydney, Australia on a work&travel visa.
Because of this he is serching for short-time work. I want to help him
a bit from overseas, via the magic of the internet :)

So I am searching for job listings in Sydney: specificaly for
unskilled/low-skill work, manual labour, part-time jobs, something
along that line.
He has the rought equivalent of a high school degree (Abitur at a
german Gymnasium), no other references, and his visa only allows for 3
months at the same job, so most better-paying jobs are out.
Unfortunately that excludes all job listings on the internet I found so far.

Where can I find job listings that fit these criteria? Or is there
another good way to find a job for him?

TIA

There's plenty of places in Sydney dedicated to finding short term
work for travellers.

Tell you friend to pick up one of the free travellers magazines from
one of the hostels, they have plenty of employment agencies listed in
them! Or check out their noticeboards (The YHA near Central Station is
one of the bigger and better ones)!

Thanks, I will forward that to him. 

(However additional tips would still be greatly appreciated.)

I would recommend backpacker job centres too. These jobs are tailored
specificially for travellers.

Sydney Backpackers
http://www.sydneybackpackers.com.au/html/jobs.html

YHA Advice on Working Holidays 
http://www.yha.com.au/australia/working_holiday.cfm

What about contacting other German-speaking people for advice?

The German Club
http://www.concordiaclub.com.au/index.htm

The German School
http://www.germanschoolsydney.com/

And here is a website covering "the German scene" in Australia,
complete with job listings.

Infobahn Australia
http://www.infobahnaustralia.com.au/treffpunkt/Jobs.htm

I hope this helps.

Viel Gluck.

* j *