Blockchain is the most popular and easy to use service of Bitcoin online wallets. The service has a strong multi-language support and displays your balance in Bitcoins and many other currencies at the rate of the exchange.
The keys are server-stored, and after the login/password pair entry, a user will get a full access to his/her wallet. Login is system-assigned, but the user creates a password himself. With every change of your network, browser or PC you will need to confirm your access by email.
The new version, recommended to previous users and used by new users by default, offers a variety of settings to ensure security, including text messages to your mobile, 2-step authorization and the second, additional password.
The service also allows customers to set the amount of transaction commission by themselves. Mobile apps for Android and iPhone are available.