Hi Laura; I think all the ones with TomTom software include advance warning of lane changes. I've got a fairly old one; the newer ones are better still, changing the view to show the details of the lane layout. TomTom aren't the cheapest, but if you don't want all the European maps and so on they can be had for about £150 or so. If you want really cheap, try Morgan Computers at http://www.morgancomputers.co.uk/?adnetwork=af . They've got TomTom at around £100, plus several others.
Tim