MoBo: Best motherboard for ~$100 right now is the
ASRock Z68 Extreme3 Gen3. It's a fantastic board. The only thing about it that I was disappointed about was that it doesn't have internal USB 3.0 headers, but it's got two USB 3.0 ports on the back, and most budget builders don't have USB 3.0 devices anyway. It also does have an HDMI output, so it should work great for you.
HDD: Hard Drives are a bit more expensive because of the flooding in Thailand, but you can still get a high quality 500GB drive for $100. My two suggestions:
Seagate Barracuda 500GB 7200rpm 16MB cache Sata III
Western Digital Blue 500GB 7200rpm 16MB cache Sata III
These guys are both top quality brands...so just kinda pick one.
RAM:
You don't need more than 8GB of RAM if you're just going to be using the computer for casual purposes. Heck, you probably don't need more than 4GB. But the crazy thing is, I searched for both 8GB (2x4GB) deals and 4GB (2x2GB) deals, and they were often the exact same price! Why not just get double the memory at no extra cost?
8GB - $30 -
HERE
This deal will also work perfectly fine with the motherboard I suggested.
As far as
cd/dvd burner goes, as long as you don't need anything regarding Blu-Ray, they're pretty much all the same. Most everyone will advise you to buy the cheapest one out there. Here's one with great reviews and has free shipping:
HERE
Since you aren't doing much gaming, I think you'll be pleased with the integrated graphics on the 2500k. They're pretty good. Hope this helps!