I always use multitran It has lots of variants for each word and a lot of phrases. Sometimes you should double-check it, because it's like wikipedia - not everything is 100% correct.

So, same strategy as with wikipedia: you go there when you run into some new fact. After reading you'll most of the time say "well, that sounds reasonable", but sometimes you say to yourself "wow... Wait a minute - that doesn't sound right". And go look for confirmation.