CardKiwi.com is a website that allows you to create and manage your flashcards. You can create flashcards with friends to add a collaborative component to the process. Check out this YouTube video to learn more.
Cram is a website that allows you to create and manage flashcards. There is an app for both Android and IOS. If you don't want to create your own flashcards, you can search their database of pre-made flashcards.
ExamTime not only allows you to create, share and find flashcards but also build mind maps and notes for free.
Fauxflash is a site that you can easily get started creating your own flashcards or search shared flashcards.
Flippity.net is a neat site that allows you to turn a Google Spreadsheet into flashcards.
Classmint is a another site that allows you to create and share flashcards. Check out this YouTube video for a brief overview.
Quizlet is a site that allows you to create flashcards. They have fun ways to study your flashcards. You can even have audio with the cards. A small fee to add images to your flashcards.