I've been researching my great-grandparents who emigrated from Eastern Europe in the 1910s. The major US-centric census sites have gotten me far, but now I've hit a massive brick wall. Are there better databases or DNA matching pools specifically for tracking down distant cousins still living overseas?

The trick with overseas research is that privacy laws in Europe restrict a lot of modern census data. You often have to rely heavily on digitized church parish registers or local municipal archives rather than the big commercial aggregate sites. DNA matching is definitely your best bet for recent connections.