Acommodation
Many hotels, hostels, motels and apartments of various quality (from no star to 5 stars) are available.
Obviously the majority of those are to be found in big cities and near popular tourist destinations, and that eastern part of Poland is less developed (and so has lower average density of hotels and such), and star rating and prices are a reasonable guide to their quality. An increasing number of those places can be found on the Internet.
Some camping sites are also available, but in the South they are opened only during summer months. In September they are already closed.
Another option for budget stays are private homes whose owners rent rooms to travellers. It is similar to Bed and Breakfast but without the meals. Prices are usually lower than at youth hostels. In major tourist destinations like Kraków and Zakopane you will see people on the streets with signs with the words "pokoje" (rooms). In countryside you will see also signs "agroturystyka" (rooms)
Youth hostels and hostels
Hostels and youth hostels are located in bigger cities and interesting areas. Many of hostels are open only in Summer.
Prices: 3 - 8 euro
Campsites
Facilities on Polish campsites are generally on a par with our UK mediocre sites (Don't expect quite the luxurious sites that you might find in Denmark and Sweden say), in the less popular areas wash rooms may be a bit on the ancient side but generally clean. One plus for Polish camping is that generally everything is inclusive, hot water and showers being free. Sites are generally only open from May - September, although there are a few that are open all year round. Campsites are located in interesting areas, and near major roads
Other
Besides campsites you can ask local people (especially villagers) if you can place a tent in their garden or near their house. I think most people will allow you to do this, some may even offer you a better place to sleep than a tent