Real estate agencies in Vienna

Have a look here https://www.willhaben.at/iad/immobilien/

This one I've good things about http://www.expat-consulting.com/Home///////

The site is in English as well

It's also a good idea, on to have an idea which district you want to live in because they all have their own Estate Agents.

Thanks for your reply! I don't know exactly in what district to move. A friend suggested that districts 1-10 are a good choice. I will try to contact some landlords directly too while I'm there. I have just received this email from an agency:

"For self-employed persons, it is difficult to rent apartments from institutions owners.
Accepting institutional owners Self-employed only with submission of a balance sheet of the year, which will not be possible for you.

I recommend Private Property Offer to request.
We currently have no matching properties from private owners."

No positive reply so far