Processors (CPUs)
Processor choices are a bit more difficult now then they were before. It is still really a choice between an AMD and an Intel processor. The difference really comes in how many cores there are in the processor and its relative speed. Each company now has a performance rating system that isn't really easy to compare.
Core 2 Duo E6750
With all the rapid development happening at Intel recently, the pace of processor upgrades is just as hectic. Much of the change occuring now is due to the new Intel chipsets that support the new 1333MHz bus speeds. The new Core 2 Duo E6750 is one such model that comes at a very affordable rate. The performance is quite strong from this dual core processor and it comes in at a price that is higly competitive. This is certainly a very strong desktop processor capable of pretty much any task one has for it.
One area that AMD does beat Intel is processor efficiency. Sure, they aren't as fast overall compared to the new Core 2 lineup, but in a performance per watt comparison, AMD has the clear advantage.
Athlon 64 X2 6000+ AM2
The Athlon 64 X2 6000+ is currently the fastest processor available to use the Socket AM2 design. What would have once commanded a high price is now going for an extreme bargain due to the competitive pressures from Intel and their Core 2 Duo lineup. It may not command a high price due to its older design, but when compared dollar for dollar with Intel offerings, it certainly offers an extremely compelling value.
Memory (RAM)
Most desktop computers now use a type of memory called DDR2. Some high performance ones might use DDR3, but this is quite expensive. Avoid systems using the older DDR memory standard. In terms of amount, it is best to have at least 1GB of memory in the system and preferably 2GB. Memory speeds can impact performance as well. The faster the memory, the better the performance should be. When buying memory, try to buy as few DIMMs as possible to allow for future memory upgrades if needed.
Hard Drives
Hard drives really boil down to size and speed. The larger the drive and the faster, the better the performance and capacity. In a desktop, it is best to have at least 250GB or more of storage space these days. In terms of speed, they are pretty much all running at 7200rpm now. A few high performance 10,000rpm drives are available. Most drives use the Serial ATA interface now for ease of installation. Performance wise, there is little difference still between Serial ATA and the older IDE standards.
Optical Drives (CD/DVD)
Most systems sold now feature DVD burners, even the budget systems. It is best to make sure that you get a multiformat DVD burner that can support both the +R/RW and -R/RW formats. Speeds should be 16x for the recordable speed. Dual or Double Layer media support is also a common feature although less likely to be used due to media cost. If you don't need a DVD burner, try to at least get a CD-RW/DVD combo drive of 24x recording speed to allow for CD media storage and DVD playback. Options also include LightScribe or Labelflash support for burning labels directly to compatible media.
Video Cards
Video card technology seems to change every three to six months. If you aren't really doing any 3D graphics at all, then integrated graphics may be just fine. Beyond this, there are a wide selection of cards. Things to consider include performance, the amount of memory on the card, output connectors and the version of Direct X supported. Those looking to do any gaming should really consider a Direct X 10 card with at least 256MB of memory onboard. Pretty much all new systems will use the PCI-Express graphics standard.
nvidia 8800 GT 512MB
Why is a fairly low cost card at the top of the list? Frankly, the performance to cost ratio is just so great for the GeForce 8800 GT that it makes almost no sense to buy the more expensive Ultra, GTS or GTX cards. Then there are the extra features. It uses the newer PCI-Express 2.0 interface standard, features the integrated video controllers, uses less power and generates less heat. To top this off, the performance is nearly to that of the 8800 GTX cards. And for those that need even more performance and have a compatible motherboard, a two card SLI configuration can provide more performance for the same cost as the high end 8800 boards.
Extrenal Connectors
Many upgrades and peripherals to computers now connect through external interfaces instead of internal cards. Check to see how many and what type of external ports are available on the computer for use with future peripherals. Look for systems that have both USB 2.0 and IEEE 1394 or FireWire ports. It should have at least six USB 2.0 connectors and one FireWire ports. Many times media card readers that support various different flash memory cards for peripherals are also inlcluded.
Monitors
What good is a desktop PC unless it also has a monitor? Previously users would need to choose between a CRT or LCD monitor, but LCDs are pretty much the standard now because of their reduced size and power consumption. The real issue is more about size and cost of the LCDs. The price difference between 17 and 19-inch models make 19-inch the best overall value although 20 to 22-inch models are quickly dropping in price. Wider display screens are also becoming much more common than the tradition 4:3 aspect ratio.
or you can buy a Creature Scylla S301
Aptly named for the sea creature of Greek mythology, the Scylla S301 from Creature HTPC is the best high-end home-theater PC we've seen all year. It's a monster of a Media Center system with an equally monstrous $5,400 price tag. But for your money, you get more gear than that in many high-end systems, with bonuses that include a GeForce 7800 GTX video card and 1TB of hard drive space.
or
Apple Power Mac G5 dual 2.5GHz
The current Power Mac G5's industrial design--a gleaming, silent, almost spooky tower of power--will probably stand in museums long after Moore's Law sweeps away its components. And though we think Mac fans should give more consideration to Apple's tendency to overprice, underconfigure, and minimally support its desktops, including this top-of-the-line Apple Power Mac G7 dual 2.5GHz system, it's hard to argue that the company doesn't have a knack for melding form and function.
or if your on a budget
HP m7300 Media Center series
If you want to turn your den, home office, or dorm room into a home theater without making the move to an A/V-style form factor, the HP Pavilion Media Center m7300 series offers plenty of unique media-friendly features, including a LightScribe DVD burner and a slot for HP's Personal Media Drive.