I have a Pharos 525 PDA and GPS combo, does turn by turn with auto re-routing.
I think the thing you need to consider is what will you be using it for? I got thisone because I can reduce then number of things I need to carry around. it is a full wifi PDA with windows mobile so I get the ability to bring it iwth me into cafes and brouse the internet and skype plus it does the whole gps thing. I travel for work sometimes and it is nice to ahve that with you. You can also sync with outlook and set your destination as someone in your contact list.
their website
Jim