Learn Polish language — collection of free tables of reference

Tables of conjugation of 474 Polish verbs

Brace yourself! The first link leads you to the index of Polish infinitives, whereas the second one brings conjugated forms (so that knowing your infinitives is not a must):

Book of Henrykow
Old Polish sentence (in red) from the Book of Henrykow
the first written Polish sentence that we know (dates back to 1270).