I currently have a GeForce GTX 550 Ti. My question is would it be better for me to upgrade to a card that can support 3 monitors (if so what card would be best) or should I buy another 550 TI and do SLI.
I enjoy gaming but not looking to spread the game on all monitors. The main purpose is to be able to run a game on one while having up other programs on te others.
I think you should have two cheap options. One, if your motherboard has on-board graphics and your BIOS allows you to select two simultaneous VGA output devices (i.e., on-board vs. PCIe), you should be able to use on-board graphics for the additional monitor.
If not, and assuming you have an empty PCI-e slot, since you don't care about SLI in gaming I would just get a second super-low-end GPU (preferably an nvidia, for driver considerations), and use that for your additional monitor(s). No need to buy a high-performing GPU if you just want another non-gaming display.