I discovered this the other day, really wish I'd discovered it earlier as I couldn't find any decent online tools to help me with my case endings.
Learn Russian online: Test Russian cases, gender and plural of Russian nouns
and
Learn Russian online: Test Russian adjectives (Cases, Gender, Comparative, Short version)
At the moment I get around 75% correct on either test, so I still need to work on it. Just thought I'd share that here, as it could prove useful to anyone else who struggles with declension