an answer buried in the middle of nowhere
Just went to hook up my monitors to my Macbook Pro Retina, one with DVI to Display Port, the other with HDMI, and my problem was immediately apparently: I was in underscan town...
Luckily I happened to stumble on an answer online, but it was a little obscure. Mind you, my monitor had the same option as the poster's monitor (a Samsung in my case) in the post below, so your results may vary, but it fixed the issue:
Okay, I was having the same problem... Trying to connect Macbook Pro to a 24in monitor... And I was SO disappointed I had to use the "underscanning" feature in the Displays box to make the bigger screen slightly smaller so it fit everything in there... This was horrible to me because it also made things less clear.
BUT I FIXED THE PROBLEM!
Go into your little settings within your ACTUAL MONITOR... And there's a section that talks about "Input"... Mine says "Input Select".. And where it mentions "HDMI", it gives an option of PC or AV... It was set to AV!! So I set it to PC and life became wonderful again! Spread the word. This seems to be a common problem but not everyone realizes it's the monitor.
The answer was found at http://forums.macrumors.com/showthread.php?t=1313094. I figured I'd toss a post up to try and make the solution a little more SEO relevant to those suffering from the same problem.