Best Graphics Card for under £100?

i need a new graphics card, scratch that, i need a graphics card, i've been using the integrated graphics on my ASRock AMD motherboard (an old NVIDIA® GeForce 7025 set up) and was wondering what you guys have to say?

i honestly DGAF if its Nvidia or AMD/ATI to be honest it just needs to be under £100 i've seen Nvidia GeForce GTX 580's fro about £80 odd and about the same or a bit cheaper for AMD/ATI HD 6970's which i think are the highest end ones i can afford.

The rest of my rig is a AMD Phenom II X6 1045T CPU, 8GB Corsair DDR3 RAM 1TB WD Black drive and a 60GB Intel SSD boot drive.

Anything you guys can suggest would be great

-Dom

EDIT : i will not be doing any gaming whatsoever on this rig its purely for light video editting and video streaming online

EDIT 2 : CPU Upgrade to Phenom II X6