The Shimano road spd pedals are good - cleatwise they have a positive and wide connection, without cleats, that wide platform allows you to pedal vey efficiently in trainers; I had to do a TT like that when I forgot my shoes and I did alright!
Shimano do some pedals that are designed to be used with or without cleats. So you can cycle in your cycling shoes clipped in properly or just in trainers, as the mood takes you:
Comments
http://www.rei.com/product/668198
Not sure if you can get em for road bikes though
http://wiggle.co.uk/ProductDetail.aspx?Cat=cycle&ProdID=-985728531&N=Shimano%20M545%20Free-Ride%20Pedals
http://wiggle.co.uk/ProductDetail.aspx?Cat=cycle&ProdID=4000000039&N=Shimano%20M324%20Combination%20Pedals