Below are some websites that may help you with the Poland side of your genealogy search.

BaSIA
This database contains more than 4 million entries from all over Wielkopolska (“Greater Poland,” in modern west-central Poland) and Kuyavian-Pomeranian. With a focus on the region in the 18th to 20th centuries, this easy-to-use database contains indexes that come from state and church archives, with some links to scanned images.

FamilySearch
Has an extensive section on Polish Research, including 41 learning courses.

Genbaza
A website dedicated to scans of Polish record books, from the archives located in Kielce, Gdańsk, Koszalin, Warszawa, Grodzisk, Mława, Pułtusk, Płock, Łowicz, Łódź, and Sandomierz.

Geneteka
Genetekais a database of nearly 25 million Polishvital records that have been indexed by surname and given name, from parishes and registry offices which are grouped according to the contemporary province in Poland in which they lie. 
A detailed, 3-part, instruction guide for the site is available here.

HalGal (Halychyna/Galicja)
This website provides general information on Halychyna/Eastern Galicia. This site should be the starting point for anyone researching their ancestral roots in Western Ukraine/Eastern Galicia.  Many of the pages will be useful for Polish researchers of Western Galicia, as well.  

Lubgens
This site is focused on the Lublin area and has a large index of the church books as well as some scans.

Metryki
A database of the Polish Genealogical Society of Poland which has scans from a few different Diocesan Archives and State Archives. This site requires registration, which is free. 

National Archives in Krakow
An online collection of things like census, church books, and civil registers

Poland GenWeb
This is a website where you click on a Voivodeship on a map and it takes you directly to resources related to that area.

Polish Genealogical Society (Polskiego Towarzystwa Genealogicznego)
Homepage of the Polish Genealogical Society, based in Warsaw.

Polish Roots
Has extensive information on Polish history, culture and genealogy, and maps.

PomGenBase (PTG)
The Pomeranian Genealogical Association provides online indexes to birth, marriage and death records for the Pomeranian and Kashubia area.

Poznan Project
The Poznan Project is an index of marriages that took place in the 1800s in the Prussian province of Poznan. This collection covers parts of Greater Poland and Kuyavian-Pomeranian.

Pra.in.ua Project
This is the largest database of Ukrainian residents born between 1650 and 1920. Western Ukraine was previously part of Poland and the Galician partition. The opening page outlines (in English) information that is available through the site. 

Projekt Podlasie
Has indexes of record books from churches, courts and notary offices from Podlasie and Masovia. 

The Central Archives of Historical Records (AGAD)
Provides access to online registry books and other digitized parish records from the Eastern areas of Poland, now in Ukraine. Has scans for the areas of Lublin and Subcarpathian as well.

Polish Origins
Article about how to obtain birth, marriage or death records from a Polish Registry office. 

Polish Museum of America
This museum is located in the U.S. (in Chicago), but has a wealth of information related to Polish genealogy.