Since I dont like spending money on apps for the wonderphone I came across NAVIFREE on Itunes - well thought I would try it - as its free -
Surprisingly good - complete with all the bells and whistles including a talking posh woman navigator. Auto day and night mode, and assorted other stuff the big boys provide. Obviously it will never be as good as a dedicated unit but to have with you 'just in case' its actually pretty damn good.
Downside its one of these wiki maps things which is bound to be pants but to be fair on a particularly horrible trip thorugh Manchester last Friday it knew all my teeny back street shortcuts and responded very quickly to direction changes so give it a try and see what you think?
(sorry if a repost)