Really depends on how much video editing and how heavy on the gaming you want to go. TomsHardware is a pretty useful site for advice on what to buy.
CPU: Core i5 2500K is good for all games (pretty much). I don't know any games that really uses more than the four threads you get on the i5 and it performs just as well as the i7 on nearly all games. If you're doing a lot of video and editing and using a lot of programs that utilise multiple threads (e.g. Adobe Photoshop) then you may want to look at the higher spec Core i7s. Depends on what you need more. If you're primarily gaming with a little bit of image/video editting then you can save some money and go Core i5 2500K.
Motherboard: Just make sure it's compatable with the CPU. I don't know all the features of each motherboard off the top of my head but the P67 and Z68 chipsets generally cover most of what you need. If you do go for an extreme Core i7 3XXX, make sure you go for the X79 chipset. Also, most mainstream and enthusiast motherboards come with 7.1 onboard sound.
RAM: RAM is fairly cheap at the moment so 8Gb is quite affordable. Obviously more is better but check how high you can go on the motherboard. I think most don't go beyond 32Gb. I don't think the speed makes too much difference in games, but I don't know for vid/image editing. Unless you use onboard graphics (which you won't) it doesn't matter too much. Just make sure you buy DDR3 and that it matches with the number of channels on your motherboard. Most of the labelled brands are fine. Also check what version of Windows you get/have. Home versions of Windows 7 have a lower RAM limit.
GPU: There's a thread about the new Radeon HD 7000 series of cards comming out in January here:
http://gamrconnect.vgchartz.com/thread.php?id=138096&page=1#
Note, NVidia and AMD/ATI have different GPU architectures. NVidia cores and AMD stream processors are not equivalent. At the moment both cards provide equivalent performance at similar price points. If you're going heavy on the video editing and gaming (as in High Res, multi display, possibly 3D) then you'll want one of the top of the range cards.
Currently an AMD HD6950 or NVidia GTX 580 are pretty high spec. If you think that's overkill then an AMD HD6870 or NVidia GTX 560 Ti will play all games at 1920x1080 and at High detail levels. I wouldn't go any lower than that though.
Display: Really depends if you're going to do a lot of 3D gaming. Bare minimum for your purposes sounds like a 24" LED.
Power Supply: Surprisingly, this is probably the most important component in your case. Make sure it's a trusted branded and that it has a high efficiency rating (80+ bronze as a minimum). When calculating required wattage:
20 Watts per drive.
100 Watts for the CPU
40 Watts for the mainboard.
40 Watts for the usual video card
100 Watts for the firebreathing video card (200 for the absolute high end cards).
Then double it for future proofing and headroom.
For a bit of extra money you can also get modular PSUs that can help with cable management and improve airflow in your case. I've found Antec generally have good modular PSUs.
Heatsinks and Coolers: CPU & GPU most certainly need heatsinks and fans as a bare minimum! As long as you buy a retail CPU then it should come with a stock heatsink and fan which is fine for most applications. The only time you really need a different cooler for the CPU is if you plan on overclocking. Liquid cooling should allow you to overclock further. GPUs already have a cooling system setup.
For RAM it's less important but most of the "enthusiast" types come with a heat spreader. It can't hurt afterall. Also, with your case, remember that if you have a lot of fans the airflow will be better but so will the dust buildup (as I've discovered recently 
)
HDD: Go for a Solid State Drive as a boot drive. Makes a world of difference.
