I use Mapfactor navigator on my Samung Galaxy S2. It's a free android app using openstreetmap maps which are updated monthly. You can choose which countries you want to download and you can use it offline so no roaming charges when abroad. It has POI's, UK postcodes, about 20 possible languages, speed limit warning etc, etc. I use it here in Switzerland and crossing the border to Germany or France, and has never let me down. All these maps are free and if you want you can download TOMTOM maps for a fee (About £30 I think), which will give you lane assist and a few other "extras".
I have a Samsung holder with charger so can fix it in the car and connect MP3 player at the same time.