In certain Mac applications, applications built on Cocoa and not even all of them, there is a little trick that you can use to select blocks of text without having to select entire lines. It looks like this:

Selecting a block of text in MS Word

To do this, before you press the mouse key hold down the Alt key on the keyboard. Once you do that, you'll be able to select any random block of text without having to select the entires lines as you would normally.

While this is a cool feature, it is not well supported. It only works in Cocoa applications. And even then, the support is inconsistent. You'll have to give it a try to see if it works for the app you are using.