My knowledge about hotels in Warsaw is somewhat limited. I haven't stayed in a hotel in Warsaw for many years, and the only firsthand knowledge I get is when I visit friends staying at a hotel in Warsaw.
That's why I will limit myself to general comments. The few hotels that I mention are here because they are well-known for the position, exclusivity or history (i.e. the most expensive). And then I will mention a few hotels where I have been by happenstance.
In order to find accommodation you may use one of the search engines at the right side.
The hotel prices depend on quite a few aspects. The most luxurious hotels charge around 400-800 zloty for a standard single room. At a three star hotel you may get a room from around 200 zloty, and it is possible to get a decent quality room outside the centre for around 100 zloty.
Try different search engines before you decide on a room. You may save quite a lot of money by spending half an hour on comparing prices.
Hotel le Regina. (61 rooms). Koscielna 12 - Right in the middle of the New Town.
A small luxury Hotel right in the centre - 5 minutes walk to Rynek.
Hyatt Regency (250 rooms). Belwederska 23 (The Royal Route).
Modern businesshotel with conference facilities, exclusive fitness centre and streamlined service.
Radisson blu (311 rooms). ul. Grzybowska 24 (By Aleja Jana Pawla II)
Modern luxury hotel in the centre.
Sheraton (350 rooms). Plac Trzech Krzyzy.
Marriott (518 rooms) Jerozolimskie 65/ 79 - Right in front of the Central Station.
Warsaw's second tallest building. A bar on the top with a fantastic view over Warsaw - recommended even if you aren't staying at the hotel.
Le Meredien Bristol. Krakowskie Przedmiescie 42/ 44. A neighbour to the Presidential Palace.
A hotel from 1898 with a lot of traditions, renovated several times and it is a top class, modern hotel, but you feel the history upon entering.
Sofitel Victoria. Krolewska 11 - On the Pilsudski Square, a few minutes from the Presidential Palace.
Belwederski. Ul. Sulkiewicza 11 - Entrance from Belwederska, right in front of the Russian Embassy.
A small and cozy hotel with a good position at a reasonable price.
Novotel Centrum (733 rooms) ul. Marszalkowska - In front of Metro Centrum. If you take a taxi then please notice that there is also a Novotel near the airport, i.e. a good bit away from the centre. A nice hotel at a reasonable price.
Hostel Tamka - ul. Tamka 30. Right in the centre of town.