From MIM Wiki
Taxis are cheap in Warsaw. But when using them, it is recommended that you only use taxis with the following: the symbol of Warsaw - a mermaid - on both front doors, yellow/red stripes affixed to the glass along the front doors, a number stuck to the side of the vehicle, a hologram with the license number and the vehicle's registration number on the upper right-hand corner of the front glass and a sticker with price information per kilometer that must be displayed on the glass of the right-hand side back door.
Current prices for taxis are (maximum rates legally permitted):
- Initial/starting fee : 8 PLN
- Day fare, in the urban zone : 3 PLN per km
- Night fare, in the urban zone and day fare on Sundays and holidays : 4,50 PLN per km
- Day fare, in suburban areas : 6 PLN per km
- Night fare, in suburban areas and day fare on Sundays and holidays : 9 PLN per km
Here is a list of taxi companies.
There is a handy free app for mobile which let you order a cab in the main polish cities, check here.