One of the most-used helper apps on my Mac is PopClip:

PopClip appears when you select text with your mouse. Instantly copy and paste, and access actions like search, spelling, dictionary and more.

I use it constantly to change case, copy, paste and for many other actions.

PopClip provides a menubar by selected text with instant access to Copy, Paste, case change and many other user-configurable actions.

Miraz Jordan @Miraz