Blank Slate Gaming Rig $900 budget

Approximate Purchase Date: Anytime, I can wait months, I still have to get some more money together but I'd like to get an idea of what to get now.
Budget Range: $900 and lower, but I can just wait a bit more and scrape some more cash together if you absolutely recommend a particular part/rig.
System Usage from Most to Least Important: Gaming will be the biggest draw. I've played with the idea of getting into music comp, butry to keep the priority in more of a mid-range relative to other components.t that isn't a priority.

Are you buying a monitor: Yes. I've noted that you folks tend to recommend monitors exceeding 20" for gaming, but I'm not sure how I feel about those sizes - seems like overkill. Give me your suggestions by all means, but I'll be quite satisfied with a slightly smaller, reliable monitor. As in 14" and up.
Do you need to buy OS: Yes, add the price of Windows 7 Home Premium (32 or 64 bit whichever is better with the system).

Preferred Website(s) for Parts: Newegg. TigerDirect. I'm open to better deals from other locations as long as I don't have to track shipping from a bunch of different vendors.
Location: North-central Ohio. However, I doubt that there are any deals good enough in my area to justify the gas prices.
Parts Preferences: Intel CPU, but I doubt you guys would suggest otherwise anyhow. No other preferences.

Overclocking: No. I'm just looking to play the games, not squeeze them like lemons.
SLI or Crossfire: Not now, probably not in the future.
Your Monitor Resolution: I don't want stunningly amazing every blade of grass, but I also don't want everything all 8 bitty (exaggeration but you get my meaning) so I guess medium-ish?

Additional Comments: I don't have any illusions of being able to play games with stunning eyecandy under this budget, and I'm not certain I'll be able to get mid-level graphics settings, either though it would be nice. The sort of games I'm looking to play are Arma (for Day Z also), BF3, a lot of shooters, but I also play stuff like Dungeon Defenders and what not.
Why Are You Upgrading: I love gaming but my Macbook really isn't cutting it (obviously lol Macbook for gaming?! haa!) and I'm at a good point in my life to upgrade to a good PC for gaming.

Your time is greatly appreciated.
P.S. I loved IkklThePickle's post, so I borrowed his format if that's okay because it was really killer and said exactly what I wanted to say. Thanks everyone!