I am building my niece a computer for Christmas, I am setting the budget between $600-$700. I already have parts like monitor, SSD, power supply, Case, RAM, etc. What do you guys recommend for CPU,MB,Video card that all three cost between $400-$500. She's twelve and just plays a few lower end games and youtube so it doesn't have to scream, but i want to give her the most gaming power for the money since as she gets older she will probably want to player better games.

Thanks.

for installing Linux?
i'd start from an intel CPU with integrated graphics.
the rest doesn't matter so much, but you might want to look out for ability to extend in the future, RAM etc. and esp. more powerful graphics when she wants to game more?

all in all i must add that young people don't seem to be very interested in non-portable computers.
some even go so far as to say "daddy has a computer. but i want a laptop/tablet."

I agree with ondoho except that I do think mobo manufacturer and model are quite important especially if she actually does keep it for years. Better components run cooler and last longer. The better performance can be considered frosting on the cake. The failure rate out of the box is much lower as well and warranty repair or replacement is usually easier. Considering what hardware you already have you should have no problems keeping to that budget. Normally I would recommend a standalone video card but for her age onboard Intel graphics are quite sufficient these days and decently supported everywhere.

Maybe I didn't ask my question correctly. All I am wanting is opinions on what people here would buy for MB,CPU,and dedicated video card if they had $400-$500 dollars to spend on just those three components, I already have all the other stuff. And no it wont be running linux, and I already have pretty much decided, but I just thought I would seek opinions here.

I just bought an ASRock J3455 with 16GB RAM. I don't play games, but I needed a low power machine in the living room for email, YouTube and web and I'm delighted with it. (Just over $200 for board with processor and graphics plus RAM through Amazon.)

Personally, I'd buy a Gigabyte or ASUS motherboard, AMD Ryzen processer and a GTX1070.

Ummm the GTX 1070 would eat up 99% of 500 bux. Thankfully the Ti is out now starting at 449 but not at all what OP seems to be looking for.

I have long been a mostly Asus mobo buyer but have dabbled a bit with MSi, Gigabyte, and this box is an Asrock Z-77 extreme and it effortlessly stacks up with any Asus I've ever owned. I'd buy another Asrock but I have my eye on a SuperMicro Enthusuast board next. I've long swore and been impressed by their server boards.

Considering OP is looking to the future expansion, and that's a good idea IMHO (8-10 years isn't unreasonable), I'd put the bulk of the money into a brand name mobo with a foward looking CPU socket and onboard audio/video. I'd even go so far as to spend up to 300USD or so on that mobo and skimp a bit on CPU for now. I say that because newer, forward looking mobos are not likely pinout compatible not only for CPU but possibly RAM before very long. Any PCI devices have been all but defunct now for over a year - few modern boards even bother to provide a single slot.

I'd recommend my latest Dream Machine, the Super-Micro C7Z-370-CG series but if OP bought that, he would likely keep it and his niece would get his hand-me-down. Here's a review of last years latest and greatest utilizing the 270 chipset (the 370 is too new for review). Even at almost 300 bux that still leaves room for a fairly hefty Quad Core i7, some even reserving substantial pocket change. In fact it would be possible to get a top quality, future safe, high performance Super Micro board AND a decent i7 Quad Core at the lowest number of 400 bux and require no additional monies for video. Embedded video ain't the weak link it used to be and frankly a 50 dollar nVidia would likely still handle any game she is presently enjoying. At 600 bux total expenditure weighted as mentioned, she could just crank up all the settings on all but the most demanding AAA titles, but that isn't ruled out as an upgrade. Win-win.

--- SuperMicro C7Z270 Review Example ---

Wow! I'd not looked for a graphics card so, wrongfully, assumed that a 1070 would now be on a par, price wise, with a 970.
i'd go with a 970 still, then. As long as it's not "4K" it would do.
i'd go AMD over Intel purely because AMD have proved they have a decent, not too badly priced, CPU out now without the complications Intel put you through finding out which SKU does what.
As for saving money, I thought I saw the OP ask what we would buy now and appeared to dismiss the (quite sensible, I thought) mention of using onboard graphics and other ways to save money.

Right now I am leaning toward Kaby-Lake, Z270 Board, and an nivida 1060 if I can make it work in budget. I will probably wait until black Friday/cyber Monday to see If i can score some deals. I haven't ruled out ryzen just yet, still looking at benchmarks.

ah, this reminds me of some colleagues discussing this -- isn't Kaby Lake fewer cores and threads than predecessor?
Also, if going Intel, only motherboards with a x or z are overclock capable. (Another reason I'd go AMD for processor)

IMHO Power Supply and Motherboard trumps CPU and Video card if for no other reason than they create the environment where they, and everything else, functions. Thus money should be proportioned accordingly.

Daedra, why would you buy a 1060 which apparently your niece doesn't yet require and eat up such a huge proportion of your budget? FWIW I have been using a GTX-760 for a handful of years and it runs Deus Ex: Mankind Divided quite nicely and that is a AAA title that came out just 1 year ago. I just yesterday bought a 1070Ti but the motherboard, PSU, RAM, sound card... in fact everything but a recent keyboard upgrade are just the same as when I bought them roughly 5 years ago. For reference sake my CPU is a measly i5-3550 which will remain unchanged until I build a whole new system in 6-9 months when I get the 370 series SuperMicro mobo.