Mapa Polski, UMP-pcPL, i.e. a decent open map of Poland
Free of charge, CC license

repo at http://tiles.ump.waw.pl/ump_tiles/%0d/%d/%d.png

I tested it with mapper 2.6.2 on a N800. It would be nice if someone could report usability with more recent hw/sw versions.

Cheers,
/burbie