Use StartSSL[1], or self-signed certificates if you just use HTTPS for admin access to some of your sites. You can easily find many online tutorials on how to setup TLS/SSL on your web server after a bit of googling, such as this one[2] on the DigitalOcean community site.
P.S. Judging from your username, it seems like you have played agar.io too much. :)
[2] https://www.digitalocean.com/community/tutorials/how-to-set-...
Edit: If you can wait until November this year, use Let's Encrypt[3] when it is generally available to the public. At this moment you can also use CloudFlare, which provides free SSL branded as "Universal SSL" if you use their CDN.
[3] https://letsencrypt.org/2015/08/07/updated-lets-encrypt-laun...