When you say streaming video to a HDTV I'm assuming you mean your PC is hooked up to your TV and you are streaming the media from either the HDD or some other source. Low power and quite are typically good qualities for a HTPC sitting near your TV/AV system.
Yeah stuff like netflix and hwat not
If that is the case, you only need an old 2.8GHz dual core and an integrated Radeon HD4200 or better will play HD content (my current HTPC setup). With todays parts I'd probably pick up one of the AMD A4-3400's since they are capable of Bluray 3D so they are capable of everything else. The lower power the better because you won't need a fan spinning fast and loud to keep it cool.
Yeah I went with the A4, I hear the lower the TDP or TWP or whatever it is, the less noise since the fan wont need to work as hard
For a case, that depends on budget and priorities. I got a small Hec 6T MicroATX case that is pretty much all black. It sits on the floor between some furniture and doesn't stand out, so that is perfect for me and it cost like $20. If you want, you can buy much more expensive cases that look a lot nicer.
The case doesnt gotta be pricy, I just cant have it be dinky and ugly and bulge out of nowhere and stuff
For a PSU I highly suggest the Antec Earthwatts 380PSU. The smaller the PSU (rated 80+) the more efficient it will be. However, it is hard to find quality PSUs smaller than the Antec. You could get a PicoPSU, and go completely fanless, but it will cost more.
Ill check that out, I just hate the very barebone looking PSUs, Im very picky
I'd get a SSD over a pretty case myself. I'd rather have silent and slightly ugly than a loud box that looks pretty, but that is a personal preference. When I built my HTPC a 2 years ago SSDs were still really expensive, but I'm looking into upgrading soon and installing a SSD.
The computer will be on often, I am ok with waiting for stuff to boot, SSDs rock definitely, Ill consider it
What I would buy ----- newegg for prices, includes rebates.
CPU/GPU - AMD A4-3400 - $80
Motherboard - ASRock A75M-HVS Micro ATX AMD Motherboard - $70
RAM - 2x2GB DDR3-1333 - $25
DVD Burner - LG - $20
SSD - Patriot Pyro PP60GS25SSDR 2.5" 60GB - $75
PSU - Antec Earthwatts 380 - $40
OS - Ubuntu - $0
Wireless Keyboard+Mouse - Logitech M310 + K360 - $45 (amazon)
Case - $45 left, so buy whatever you think looks nice. With this setup you need to make sure it fits a standard ATX power supply and a Micro ATX board.
Now, you didn't say if you need to buy window (home premium OEM is $100). If you do need windows for Netflix, then you may need to scratch the SSD and buy a cheap HDD.