I wanted to build a mid-range gaming PC on a ~$900 budget. I don't need ultra settings on every single game, but I wanted to have something that could withstand the test of time while still producing solid results. I'm very happy with how it turned out! My total price came in at $898 (could have gotten things cheaper, but Newegg was convenient and not terribly far off on prices).
I'm very happy with the i5 - I don't plan to overclock right away, but as the system gets a bit older I know i'll have the option to postphone upgrading. The MSI 7870 is a beast of a card, I don't think you can get much better for the money right now. Also running that at stock settings and had no problems running Planetside 2 with everything maxed out.
My budget meant skimping on a few things, but I tried to minimize the damage. My biggest hit came by option out of an SSD. I plan to get one for the OS/a few games, but I'll probably just wait until the prices drop a bit. The mouse that came with the keyboard is kinda crummy, but for $25 bucks I think I could have done much worse. I was actually fairly impressed with the Challenger case, but cable management is very limited - I barely managed to squeeze the right side of the case back on, and I'm still not completely satisfied with how it looks inside. But, airflow is nice and my temps are pretty good so I'll take it!
I'd love to hear any feedback or suggestions, and if you've got any questions for me about the parts I chose I'd be glad to help you out!