I’m a big Evernote user. It’s a powerful commercial program that allows you to sync text, photos and documents across multiple devices. Sadly, there’s no native Linux client. Also, it’s a proprietary software package, and that bums me out.
Simplenote has been an alternative to Evernote for quite some time now. It’s created by Automattic, the folks behind WordPress. It’s designed to sync only text-based notes, but that’s usually all I want anyway. Recently, the developers at Automattic decided to release Simplenote as open source! They also compiled binaries for just about every platform out there, including Linux!