Well the motherboard supports pci 16 and pci 2.0 so either card would work. The things you need to consider before buying a card is

1. Size (If the card will fit into your desktop

2. Your power supplys wattage and psu connections (make sure your psu has the connections your card requires)

3. Cost (How much do you want to spend)

4. Future intended use

The reason I didn't suggest a particular card is I don't know what you want to budget on a card
and I would suggest to you if you never intend to play resource hungry games or run graphics programs like photoshop then why would you need a great video card?

The reason you need great video card is for Vram, Pixel shader capabilities Clock speed etc etc for resource demanding games and apps.

If your youtube videos are not playing to well. I can assure you your onboard video graphics is not to blame. The problem most likely lies in your internet connection

If your downloaded music videos are not playing well then update directx to the latest release and update your onboard graphics drivers.

I have never seen a newer onboard graphics engine that wouldn't run videos

Also when deciding this graphics card guide might be helpful

http://www.tomshardware.com/reviews/best-graphics-card,2118-7.html