I use a CX 500M for my GTX 750ti, would recommend 600-750 watts for a GTX 970, just to be careful, and especially if you want to overclock.
600w:http://www.newegg.com/Product/Product.aspx?Item=N82E16817139048
750w: http://www.newegg.com/Product/Product.aspx?Item=N82E16817139142