This is how to make web pages fit to your screen

[Mint]

I'm not sure if this is only a problem on the 27" (with it being so huge) but you will notice that everything seems so small on your Mac when viewing windows in more or less full screen.

Right click the toolbar just above the URL box, click "Customize toolbar".

A box will drop down, you need to drag the zoom tool into your toolbar.

All done.

Now you just need to press the big A and your screen will magically transform into how it should be. If you only ever have 1 window open at a time, you are just wasting the rest of your screen by viewing the everything in such a small form. Enlarging it actually makes it all fit to your screen, it makes the screen look much more complete, fuller and clearer.

 

[MYmacROX]

Or if you have the magic mouse with your 27" iMac, you can use this method to zoom:

Screen zoom
Hold down the Control key on your keyboard and scroll with one finger on Magic Mouse to enlarge items on your screen.

 

[cradom]

You don't need a Magic Mouse to do that. My Logitech does it just fine. It's built into the system.

 

[CrimsonRequiem]

Command + does the same thing? >_>