APPROXIMATE PURCHASE DATE: Pretty much this week.
BUDGET RANGE: £80
USAGE FROM MOST TO LEAST IMPORTANT: Gaming
CURRENT GPU AND POWER SUPPLY: Graphics Card : ATI Radeon 6570 1gb DDR3 with HDMI Hyper Memory Upto 2gb. Power Supply: 450 Watt Branded Power Supply
OTHER RELEVANT SYSTEM SPECS: AMD FX(tm)-4100 Quad-Core Processor, 8GB GDDR3 RAM, Gigabyte M68MT-S2P Motherboard.
PREFERRED WEBSITE(S) FOR PARTS: Any website that provides logical prices, rebates, shipping, legitimate business, etc..
PARTS PREFERENCES: just looking for a cheapish decent graphics card
SLI OR CROSSFIRE: Either or depending on the cards recommended for best performance, etc.
MONITOR RESOLUTION: 1440 x 900
ADDITIONAL COMMENTS: looking at Radeon HD 7750 but not sure if it would work, it is within my pricerange and supposed to be decent for the price but if anyone has better suggestions or one that would work better I am happy to hear them.
A Radeon 7750 does seem to be the best in your price range of £80, although for £90, you can get a significantly better Radeon 7770. Can you give the exact model of your power supply? Overall wattage rating, perhaps surprisingly, is not very helpful in determining what a PSU is capable of.
Wattage doesn't prove anything. If its a crappy 450W, then it's not necessarily enough. If it's a good 450W such as at least a CX 450 or better, then it'll do the job.
Also, the 660 Ti uses far more power than the 7850. The 660 Ti uses only marginally less than the 670 which uses only marginally less than the Radeon 7950. It's best to have something more like a decent 520W or 550W such as an Antec 520/550 or better for the 660 Ti unless you're pairing it with like some weak low-power Pentium.
EDIT: also, the worst 7750 is a huge jump over even the best 6570. The 7750 that I suggested was far better than one of the worst 7750s too, granted it's not the best 7750 either. It's more than twice as fast as OP's current graphics. If we went by Tom's tiered recommendations, a three tier upgrade is a good upgrade, yet this is more like a six or seven tier upgrade.
That is not a name brand psu that I know of.
Still, it has the requisite power leads and is advertised to be able to deliver 28a, so you should be ok.
If you find artifacts or other strangeness, then change ot the psu which will be the likely culprit.