If you have a Mac computer and need a little more extra multitasking power, head over to Amazon and pick up the Corsair 8 GB DDR3 Laptop Memory Kit CMSO8GX3M2A1333C9. If you opted to do this at purchase you probably forked over $200 to Apple in exchange for 8GB of RAM.
Confirmed by the comments, these memory modules are compatible with all 2011 models. This includes the iMac, Mac Mini and Macbook Pro units. I opted to purchase two and so that I could max out my 2011 Quad Core iMac. The 2011 iMacs have 4 Ram slots. If you want to use this with your existing memory you could. Look forward to an installation video too. In the mean time, head over to the shop link below and pick up some RAM.