Stamp Catalogue by Evert Klaseboer- Images by Country (some images not there?)
http://perso.club-internet.fr/klaseboe/catalog.htm

Images of some Polish stamps
http://www.sandafayre.com/gallery/country_307_1.htm

Joseph Luft's Philatelic Resources on the Web
http://www.execpc.com/~joeluft/resource.html

Information About Local Issues (in general)
http://www.stampshows.com/local-post.html

Overprint Dictionary (in general)
http://www.askphil.org/b28.htm

Stamp Identifier (in general)
http://iswsc.homepage.com/iswsc_identil.html

Weird stamps page- Helpful site to identify unusual stamps of the World
http://www.raster.it/stefano/a/hyciywsaatsthopo.htm
 
Central Lithuanian Stamps-In Lithuanian
http://www-public.osf.lt/~ronas/zem_0.htm

Polish Stamp Collecting
http://www.polonia.net/katalog/rozrywka/filatelistyka.html

Silesia Collectors
http://www.kk.silesianet.pl/

Polska Poczta Balonowa a nice collection of Post Cards
http://www.man.poznan.pl/~stanecki/balony/poczta/poczta.htm

Early Polish Stamps
http://www.eis.or.jp/muse/yasuka/01/stamp/poland/poland.html

Jennifer's Polish Stamp Page
http://www.geocities.com/Heartland/Plains/4049/stamps/poland/poland.html

Collector from Poland (off line?)
http://www.free.com.pl/piotrna/

User's Stamps (many countries)
http://www.postage.dk
 
Alan Anderson's Internet Stamp Store (many countries)
http://www.halcyon.com/alana/poland.html
 
Old Polish (and other countries) Covers and Stamps for sale (with images)
http://www.sastamps.se/WEN7.HTM

Dealer of Polish items
http://www.jbarefoot.co.uk/stamps/pol1.htm

Dealer in Russian Areas
http://www.trevorpateman.co.uk/

Cherystone Auctions- First quality worldwide stamps, but expensive.  USA.
http://www.cherrystoneauctions.com/auction.htm

Collection of dealers stamps of all countries.
http://www.zillionsofstamps.com/