I've mostly used Anki for learning Japanese, so I'm biased towards that specific language. There are however some awesome free tools floating around that take the pain out of creating flashcards:
-[1] EPWING2Anki creates flashcards from a wordlist and a dictionary in EPWING format
-[2] Sub2srs creates flashcards based on a movie and subtitle files
It's also possible to use e.g. spreadsheets to mass-create cards. Further tools analyze e.g. a selection of ebooks and create word frequency lists of unknown words, Combined those tools have greatly assisted my progress.