Check out the Frontends subforum for good suggestions on software. Some GPS programs work better with certain frontends. All but 2 are free. StreetDeck and Centrafuse are expensive but apparently good and have nav built in. RoadRunner is my favourite but you need to buy a GPS program as with all the other frontends (iGuidance 4 is popular).
But remember, just because it is popular, doesnt mean it will be good for you. You can download all the frontends (including the pay ones) for free to test them out and see how you like them.