Good graphics cards for 250W max?

I have a Lenovo H520 computer with a 250W max power supply. It has 6G of ram, 64-bit operating system, and a 3.4 gHZ processor. I am looking to upgrade the graphics card, and I was wondering if there are any good ones of at least 1 GB that are fairly cheap, but reliable. It would be primarily for gaming, but I don't need one of those $5600 ones, just a nice reliable one of at least 1 GB. Also my computer requires a slimline graphics card, or one capable of becoming one. Thanks so much for responses and if possible, links would be great!

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