Paste - Clipboard history manager for your Mac
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Paste is a new way to copy and paste for your Mac. It keeps everything you've ever copied and lets you use your clipboard history anytime you need it across all your devices.
UPD: Please check out Paste 2!

Replies
I rarely shell out money for any kind of software, but while there are great free alternatives (e.g. Flycut), I haven't seen anything close to the performance / usability / UI in Paste. For $10, great deal.
Pros:Slick Apple-style UI, useful features, smooth performance, pinboards, search, attentiveness to UX
Cons:The window is a bit larger than necessary; a lot of space is given to show the source app of the copied item; usually not important