Best place to buy 4GB RAM for 15″ Macbook Pro?

It's the first Mac I will own, it's refurbished and I haven't bought it yet, because I'm having RAM issues, but here are the specs. It's ,299 and has the same price as a refurbished Macbook Pro 13 inch, but 2 GB less RAM.

Refurbished MacBook Pro 2.4GHz Intel Core 2 Duo

15.4-inch LED-backlit glossy widescreen display
2GB memory
250GB hard drive
8x SuperDrive (DVD±R DL/DVD±RW/CD-RW)
Built-in iSight camera
Illuminated keyboard

Do I have to use specifically have to use Apple RAM, or can I use brands like Crucial or Kingston? As cheap as possible without being fake please. Make sure that you or somebody you know has bought from the company before so I don't run into problems. Thanks!

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Tags: 13, 15, apple, display, dvd, hard drive, keyboard, Mac, MacBook, MacBook Pro 13, memory, RAM, screen, superdrive