If you are on a budget and want a decent graphics card that offers good performance to play your latest games on playable frame rates then have a look at Geforce GT 640 from Nvidia. This card has some horse power and can deliver acceptable performance even in the latest power hungry games.
GT 640 is based on the latest kepler architecture which is today the most advanced architecture found in the high end cards. It is a DirectX 11 graphics card and has 384 cuda cores. Cuda cores are the main driving force of the GPU (Graphics Processing Unit) of the card. They are also known as shader processors and more the cuda cores, the better or powerful the card is. Graphics clock in this card runs at 900 MHz (this can vary according to the card manufacturer) and it comes with 128-bit DDR3 memory which is decent for a budget level card. It supports Pixel Shader version 5.0 and OpenGL 4.2. It is priced at around $100 mark. It is a good card the price and you can play the latest demanding games at low-medium settings at 1024 x 760 resolution with Anti-aliasing turned off. There is another entry level card just under GT 640, which is GT 630 and comes with 4 GB of RAM. GT 630 has only 96 cuda cores and is way too weak to run the current high end games even at the lowest level of details, therefore go for only GT 640 if you want a budget card that can perform.