The Performance Desktop
Laptops are small. When it comes to computer hardware, size is the enemy of power. A big beefy processor will inevitably produce a lot of heat, which is why there's no quad-core Core i7 processors available in laptops with displays under 14 inches.
Because of this, some students might find that purchasing a laptop adequate for their needs means buying a 15.6" model, and one that's expensive. Graphics design students, for example, may need the power of a larger laptop in order to run the programs used in their trade.
Such large laptops are heavy and unwieldy, however. A better solution may be purchasing an inexpensive $500 or $600 ultraportable and then a separate desktop. This provides the best of both worlds, and while this may seem pricey, the overall cost will be much less than the price of any laptop capable of keeping up with a $800 desktop.
Intel processors again remain the best choice. The Intel Core i5-2500 will likely be your best choice, as it provides the latest quad-core Intel performance without costing a fortune. The Core i7-2600 is another great option, but isn't as attractive from a value standpoint as the i5.
You may be tempted to go with 8 GB of RAM, but you probably don't need to. There's a very limited selection of programs that require more than 4GB, and students likely to be using such specific software likely already know that it's a memory hog. Hard drive size is your choice, as you can find sizes from 500GB up to 1TB as well as desktops with multiple drives. I do recommend a 7200 RPM hard drive no matter what storage capacity you desire . A solid state drive is an excellent choice if you can afford it.
Discrete graphics cards will be an option. The AMD Radeon line is the best choice at the low-end, but the Nvidia GTX 560 is a competent mid-range competitor. Hardcore gamers will be equally happy with cards like the Nvidia GTX 580 and AMD Radeon 6970, but I doubt you'll find such cards in a desktop priced under $1000.
Most desktops will be available with a monitor or choice of monitors. A 22" model is a good choice. You'll probably be able to afford one with 1080p resolution, but this isn't an absolute requirement. The lower common resolution of 1650x1080 is adequate.