Diffusers can work great or for a small cheap option I have had some sucess with these
http://www.ebay.co.uk/itm/Pro-JYC-Am...oAAOSw-zxWoeU1
Not that one in particular, but get the correct one for your flash. I have no idea about that seller.
You can get different colour lids.
They are quite inexpensive and work well in some conditions. I use one sometimes for insect macro work.
Or as Jeff says, bounce of ceiling may do it. Just watch white balance if ceiling is not pure white. Mine give a nice primrose hue to the pictures