TL;DR:
The more you pay, the more features you get. Things that say "2.4 GHz, 3.4 GHz+" or "dual core, quad core" processors are good for a laptop. Installed RAM should be 4.0. System type should be 64-bit. Apple products, although lightweight, are overpriced as hell and are more or less used for creativity rather than business. Your memory will depend on your intentions for the laptop; 400GB is fine for daily life.
Long version:
Usually, the higher-priced the laptop is, the more features it has.
If it's priced $600-$1,000, you're looking at something that not only gets the job done, but will last for a long time. It will depend on the brand that you choose, too. HPs are cheaply priced, as is ASUS. Some of Toshiba's products are often overpriced as is SONY; however, SONY is fabulous. Apple is an option, but they... are too damned expensive.
Generally speaking, you'll find more HP products and Toshiba products, if you go to a store. And, it will only be a few select models. ASUS will also be available, but only a few.
If you go for something that's ~$200-$400, you're most likely looking at a small, but efficient product that is generally OK for work and school. Its power is not ideal for multitasking many programs, and if it's used daily, then the laptop will die.
2.0-3.0+ GHz is good for the processor. You may see "dual core" and "quad core." The "quad" is better than the "dual," but if that's all the processor has, then that's fine.
In terms of installed RAM, you'd be comfortable at 4GB and a 64-bit machine. 32-bit machines can go up to 4GB, but it would be nearly impossible to upgrade the RAM in the future, since it is the type of operating system. With 64-bit, you will have the opportunity to double your RAM.
The RAM allows you to play RS and multitask other programs all at once.
In terms of space, it depends on what you are going to use it for. If it's for work/school, 200-400GB+ is good.
