Encrypting files locally before sending them across the Internet can be a hassle. However, the only means by which reasonable assurance of confidentiality and privacy in regards to Internet communications is via encryption. Fortunately, there are other options.
One of those secure options is to use an encrypted e-mail service. There are many of these available, some offer the service for free for low volume personal use and a paid version for high volume commercial use. One such service is hushmail.
Services like hushmail offer encrypted e-mail communications. However, that security is only provided between you and other users of the same service. Thus, you and your recipients will each need to sign-up for an account and then be careful to only send the sensitive messages to and from your hushmail account.
Another variation of encrypted e-mail is to use PGP or other client-side encrypting add-ons to your e-mail client. PGP and GnuPG can be installed into most e-mail clients, such as Outlook and Thunderbird. They do not work with e-mail accessed through a Web browser. These tools can add the abilities to encrypt and digitally sign e-mails. The security of PGP/GnuPG provide protection across the Internet for your messages. However, the recipient must be running a PGP product on their e-mail client in order to decrypt messages or verify your signature.