I usually feed mine pellets from P@H but there are other brands around such as A&P and Excel. Generally, you want pellets with a high fibre content. You should also give as much hay as they want to eat because getting lots of fibre in is important to keep them healthy. Their diet should be 80% hay, and 10% pellets and 10% veg.
Mine get pellets in the morning and veg at night and are out in their run during the day.