I pulled out the original RAM from Apple's latest (non-Retina) Macbook Pro, and am selling it for half what Apple charges to do the upgrade. Two 4GB sticks, so 8GB total

Here's the description from Apple's website:

Memory
More memory (RAM) increases overall performance and enables your computer to run more applications at the same time.
The more memory your computer has, the more programs you can run simultaneously, and the better performance you'll get from your computer. Increasing the amount of memory in your MacBook Pro is an easy way to improve performance.

How much memory is right for you?
Choose the standard memory to support day-to-day tasks, such as email, word processing and web browsing, as well as more complex tasks, such as editing photos, creating illustrations and building complex presentations.
Max out the memory in your MacBook Pro with the 8GB option to enjoy the greatest possible performance for all your computing tasks.
MacBook Pro uses one of the fastest memory technologies available today -- 1600MHz, Double Data Rate (DDR3), synchronous dynamic random-access memory (SDRAM) -- ensuring that the Intel Core i5 and Core i7 processors are constantly fed with data without wasting clock cycles.