Online Russian declension table!
My Russian friend sent me this part of Multitran that's not easily found in English Google or through its main page. You can easily write a noun/adjective in any form and it will tell you what case(s) it can possibly belong to, as well as if it's singular or plural. It will also display the various other forms of that word.
It's also a verb conjugator.
The site is in Russian so it'll be helpful to know these vocabularies
падеж = case
Именительный = Nominative
Родительный = Genetive
Дательный = Dative
Винительный = Accusative
Творительный = Instrumental
Предложный = Prepositional
единственного = Singlular
множественного = Plural
It seems it is computer generated so use your discretion in terms of its accuracy.
This site is very good for declensions and conjugations too. It indicates where the accent falls.
[added] Type the word that you need declined or conjugated in the little box and push View. You will be given a new tab with all the forms of a word. For instance, for nouns there will be all of the cases, singular and plural, for verbs there will be all of the forms, including participles, etc., and as I mentioned, the stressed syllable is indicated.
It is really only good for forms, as the dictionary meanings given are minimal, but it is great for that, and after getting further along in to the Duo course it will be more useful. (There is some information, too, about how the word's type is classified [little letter codes] that can be ignored.)
Note: I changed the link so that the interface is in English.
This one is super good, my favourite by far!