In Russia, I support and plan to join AKM (about 5000 members) and RCYL(b) youth groups. As for general parties, I guess I support the Russian Communist Workers Party- Revolutionary Party of Communists (RCWP-RPC), of which RCYL(b) is the unofficial youth group. I mention it quite often in the articles that I post. Now, judging from everything that I have read about RCWP-RPC so far, they are very decent and are probably the only anti-nationalist, a real Marxist-Leninist workers party in Russia right now. However, they are not as progressive socially as they could be in some fields (like homophobia, which is common in Russia, but still anti-nationalist, anti-racist, anti-religion, anti-KPRF, anti-reformist/revisionist, very democratic, etc.) so that is why I am looking more at youth groups. In Germany, I agree with Rjevan.
Wiki about all of them:
AKM,
RCYL(b),
RCWP-RPC