It would be easier if i knew where you lived and also what size tower you want but ill start with this if it's not enought ill gte a better one.
Case: With a Case you need to make sure it fit's your style and you original blue print's for a gaming rig you need to go ATX or even better full ATX. The case has to have a lot of room fo rbig grapichs card's and other bigger compnenet's, so for your case i have chosen the Zalman GS1000 gaming tower. This tower should be able to give you amazing cooling as zalman are on the pinnacle of PC cooling and it is also a tool-less case meaning you won't need any tool's to install hardware.
Link 1: http://www.novatech.co.uk/novatech/specpage.html?ZAL-GS100B
Link 2: http://www.xcase.co.uk/p/574892/zalman-gs1000-black-gaming-case---3-x-hotswap-hdd-.html
Monitor: As you know without a monitor you won't be playing many game's so you need to make sure to get a decent monitor, even more so if your going to use it for media, So i have chosen a nice samsung monitor as it is very good piece of kit for the money and damn sexy. And it dosent end there it even has a stupidly high contrast ratio so you will know the colours you are seeing are down to the last pixel.
Link 1: http://www.novatech.co.uk/novatech/specpage.html?SAM-SM2433
Link 2: http://www.ebuyer.com/product/150964
Motherboard: To play high end games you will need a good motherboard working the strings from the background so i have chosen a very good fast reliable one to keep you going for ages.
Link 1: http://www.novatech.co.uk/novatech/specpage.html?GIG-EP45S4
Procesors: Anything you do on your PC will use you processor so you need to make sure you get a good one even more so if your going to be gaming or running multiple aplacation's, So for this purpose i surgest going for the intle q6600 as it a very nice quad core processor and can be clocked to very high amount's.
Link 1: http://www.novatech.co.uk/novatech/specpage.html?IL-Q6600E
link 2: http://www.ebuyer.com/product/131950
PSU (power supply unit): Depending on what you don on your PC will decided on what wattage you will need your PSU to give, because your gaming i have given you a nice 700Wat PSU as that will alllow you to run multiple graphics cads in either Nvidias SLI or ATI's crossfire.
Graphics card: Now of course we come onto the main area of intrest to most people looking to buy a gaming PC, For this i have chosen a Nvidia card called the GTX280 this card will be able to run any game you can throw at it and also clocks in higher in benchmarks against the new ATI 4800 series. *i will post the benchmark results in another link*
Link 1: http://www.novatech.co.uk/novatech/specpage.html?BFG-GTX28O
link 2: http://www.ebuyer.com/product/152514
Link 3 (benchmarks): http://www.tomshardware.co.uk/charts/gaming-graphics-charts-q3-2008/Sum-of-FPS-Benchmarks-1680x1050,798.html
Ram (random accses memory): Now you msy think RAM isn't that important but youd be very wrong to think that as evry good gaming rig has good RAM in the background.
link 1: http://www.novatech.co.uk/novatech/specpage.html?OCZ-8500PT
HDD (Hard disk drive): This one is kinda simple the only thing you need to watch out for is the RPM of the hard drive if it's to slow you will k now about so i have given a terrabyte of memory whihc is 1024GB of space, with a good RPM to stop you from having slower speeds on your PC wehn your hard drive is loading.
Link 1: http://www.novatech.co.uk/novatech/specpage.html?WD-1001FAL
I will add a bit more later but is that ok so far.