Pretty much all cards under $50 would be fine in a prebuilt with a 300w PSU, however you really should post full system specs if you want an accurate opinion (and also if you wish us to verify that its compatible). The 8400 above is an old card. You will be better off with newer technology.
The 210 above is a good choice for your needs. Another good choice would be an AMD 6450. http://www.newegg.com/Product/Product.aspx?Item=N82E16814150581