Honestly, if you're going for a budget system to play current midrange games at full detail, $1500 is overkill, even if you need all of your peripherals. Since Newegg exists in Canada, so you're covered the same as we in the states.
I'll throw an experimental price-only budget build (an actual budget build, mind you... not a $1400 middle-top system) up here... but I'm not doing compatibility research here, so you'll most likely need to swap a part or two out for something in a similar price range:
[edit]
What lies below is the thought processes that took place before I was corrected a couple of times.
this post was the eventual conclusion [http://www.escapistmagazine.com/forums/read/9.378476-Right-Building-a-PC-thread?page=3#14804768].
[/edit]
-Proc: AMD Phenom II X4 955, 3.2Ghz, Socket AM3, quad-core, 95W [http://www.newegg.ca/Product/Product.aspx?Item=N82E16819113007]
$109.99
-Mobo: ECS IC780M-A2 [http://www.newegg.ca/Product/Product.aspx?Item=N82E16813135250]. Honestly, not a lot of good options for AM3 boards on Newegg.ca, but there aren't a lot of good budget quad-core processor options that aren't AM3s. The ECS isn't an ideal choice, but it has very good reviews. More importantly, it has no onboard video (which can be a pain in the ass to disable, depending on the BIOS the manufacturer goes with. Bad idea on your first build). If you find a better one elsewhere (preferably an Asus or a Gigabit, apparently MSI is dodgy this generation), go with that. Apparently ECS is a pain to deal with if you happen to get a bad board. My roommate calls this "cheap Chinese crap".
$54.99 or...
-Alternative: ASUS M4A88T-V EVO AM3 880G [http://www.newegg.ca/Product/Product.aspx?Item=N82E16813131827]. In case you don't mind disabling onboard video (might be a pain, might not. Either way, it'll be a better motherboard): . The more I think about it, the more I'm sure I should remove my first recommendation, onboard video or no. I'll leave it up in case you find my thought processes on the matter useful.
$89.99
-RAM: G.SKILL 4GB (2 x 2GB) DDR3 1333 (PC3 10600) [http://www.newegg.ca/Product/Product.aspx?Item=N82E16820231180]
$31.49
-Alternative: Crucial Ballistix 4GB DDR3 2000 (PC3 16000) [http://www.newegg.ca/Product/Product.aspx?Item=N82E16820148457] If you go with a motherboard capable of DDR3-2000 (like the Asus I linked):
$51.99
-Vid card: GIGABYTE GV-N460OC-1GI V3 GeForce GTX 460 (Fermi) 1GB 192-bit GDDR5 [http://www.newegg.ca/Product/Product.aspx?Item=N82E16814125412]. Chosen more for noise, heat dissipation and stability than speed, although it has more than enough of that for your purposes (even my old 7950GTX can run TF2 on full... and it's old now).
$139.99
-Case: COOLER MASTER HAF 912 RC-912-KKN1 Black SECC/ ABS Plastic ATX Mid Tower [http://www.newegg.ca/Product/Product.aspx?Item=N82E16811119233]. Upside: very modern, modular, friendly for first-time builders who don't want to do any metalwork on their case... also very good cooling right out of the box.
Only downside: it's all plastic on the outside. Tough plastic, but still plastic. Don't drop it down a flight of stairs.
$69.99
-Power Supply: COOLER MASTER Silent Pro M600 RS-600-AMBA-D3 600W ATX12V Modular [http://www.newegg.ca/Product/Product.aspx?Item=N82E16817171036] this may actually be overkill for this system, but you're always better safe than sorry when dealing with power supplies.
$109.99
-HDD: SAMSUNG Spinpoint F3 HD103SJ 1TB 7200 RPM 32MB Cache SATA 3.0Gb/s 3.5" [http://www.newegg.ca/Product/Product.aspx?Item=N82E16822152185]. Side note about hard drives... since most of 'em are made in Japan, prices have gone up and reliability has gone down in recent years... since the earthquake. There's about a 10% failure rate no matter what brand you buy nowadays, unless you spend the ludicrous amount of money necessary to get a decent sized solid state drive.
$79.99
-Optical Drive: ASUS 24X DVD Burner [http://www.newegg.ca/Product/Product.aspx?Item=N82E16827135204].
+$20.99
=$672.92
-OS: Microsoft Windows 7 Home Premium SP1 64-bit - OEM [http://www.newegg.ca/Product/Product.aspx?Item=N82E16832116986]...you'd totally be able to get what you want running under Linux for free, but that would take a lot more work. Soon as Steam and Source go Linux native, it'll be no work at all...
+$109.99
=$782.91
Now, for your keyboard, mouse and monitor... it's mostly a personal ergonomic choice, though there are some monitor brands to avoid for their failure rate. My opinion on the matter may not mean much to you or most folks on this site. I've been building systems for close to 20 years now and I'm set in my ways.
I like a 2-button corded optical wheelmouse. They usually cost $15 new, $5 used around here.
The keyboard layout I use for gaming has fallen so far out of vogue, you can't find it anymore... but just about any flat, $10 keyboard should do you fine. If you want a specialized gaming keyboard, expect to pay around $80.
My eyes are so badly damaged, I may as well not have peripheral vision for other than movement, so I like 19" 4:3 monitors. this [http://www.newegg.ca/Product/Product.aspx?Item=N82E16824116463CVF] is what I would choose,this [http://www.newegg.ca/Product/Product.aspx?Item=N82E16824116437CVF] is a widescreen equivalent, and this [http://www.newegg.ca/Product/Product.aspx?Item=N82E16824116439CVF] is closer to what most people would recommend. Oddly enough, they're all close to the same price point.
I'll just assume you want the HD monitor, so
$174.99
Also, that one has speakers built into it, so no need to worry about those unless you want surround sound.
Assuming ~$150 for your mouse and keyboard... this is, at a maximum an $1100 build. Much more than I expected, but I never have to account for mouse, keyboard, speakers, monitor or operating system. I have those just laying around in great numbers. For me, it would be just under a $700 build.
Also, I'm working with what I know here. You may be able to get better performance for your dollar from an FM1 board build... I just have zero experience with those.
One thing about going Intel... only if you want top-end stuff. They've got the speed advantage, but expect to pay double for the same bang if you're not buying top-end stuff.
Went over a few things with my roommate, and if you want to build something a bit faster and more expandable with an FM1 board/processor (which is what AMD is still developing for), he recommends these:
-Proc: AMD A8-3870K Unlocked Llano 3.0GHz Socket FM1 100W Quad-Core Desktop APU (CPU + GPU) with onboard AMD Radeon HD 6550D [http://www.newegg.ca/Product/Product.aspx?Item=N82E16819106001]. The on-chip video here will apparently disable itself in the presence of a dedicated GPU.
$129.99
-Mobo: GIGABYTE GA-A75-UD4H FM1 AMD A75 (Hudson D3) HDMI SATA 6Gb/s [http://www.newegg.ca/Product/Product.aspx?Item=N82E16813128515]
$117.99
He also scoffed at my hard drive choice (with good reason). Recommendation:
-HDD: Seagate Constellation ES ST500NM0011 500GB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Enterprise Internal Hard Drive [http://www.newegg.ca/Product/Product.aspx?Item=N82E16822148756]. Half the space, a bit more expensive, much better speed... a bit noisy, but also less likely to be dead on arrival. As an enterprise drive, it's designed more for business systems, with access speed and longevity in mind. If you need more storage space later, you can always add drives. No need to worry about space now.
$104.49
Everything else would remain the same. This would improve the build quite a lot at a cost of $72.50.