Whats your budget? If its about 100 bucks the R7 250 is what you wanna get, I'd recommend the 250x if you have a better PSU but I wouldn't risk it.
If you only have about 50 bucks... Well... I guess grab a used 6670 from ebay?
But you never asked about a replacement card so feel free to discard this post. (heh, discard)