The plain text editor Simplenote is an excellent way to take notes and sync them across a variety of devices. Metanota is a simple but visually appealing Mac client that makes taking and organising notes easy.
It's no secret we love Simplenote and while a few Mac desktop options exist, notably Notational Velocity, Metanota looks good while retaining a lot of key features. It has a simple interface that integrates nicely with OS X and it's easy to use. More importantly, it has a robust folder feature and offers simple tagging of notes. The folders make it incredibly easy to organise your notes and you'll find them on other clients (like iOS or Windows) marked as tags. If you're a heavy Simplenote user, Metanota is worth giving a look considering the ad-supported version is free in the Mac App Store. If you like it you can ditch the ads for $3.99.