Finding accommodation in Warsaw shouldn't be very difficult. There are many options available and the only criteria is how much money you are willing to spend.
Flatsharing is definitely the cheapest way of finding accommodation. It is especially popular among students and young professionals.
In case of partnership, people who have signed the lease are the only legal tenants, and therefore are responsible of the accommodation (it is possible to let the landlord know of this partnership if officialised by the town hall for example).
There are a few good sources of finding accommodation for your stay.
This is the best choice if you want to find accommodation quickly and without stress. However it is also more expensive way, as real estate agents will usually charge you a fee or add it to your rent.
For the most comprehensive list of real estate agencies in Warsaw and region visit http://www.oferty.net/
Update 6/02/2015
Looking for cheap accommodation in Warsaw isn’t easy and can be time consuming. Fortunately the times of browsing innumerable adverts, making hundreds of phone calls and visiting dozen of houses belong to the past: with Uniplaces now you can look for your room comfortably sitting at home. You can pick a room in a shared home with other expats, a studio flat if you want more privacy, or you can team up with other friends and rent an entire apartment just for yourselves.
The booking system is very simple and doesn’t require any visit: all can be done in advance thanks to the detailed descriptions and photos of the rooms and you can secure your room before even getting there. Moreover the Uniplaces team will be available for any questions and help.
Uniplaces is an online marketplace for booking mid-long term accommodation with thousands of verified properties.