It seems to me that iGO Primo 1.2 on Windows Mobile is about the best of the bunch right now. If someone wanted to pay good money for it, where and how can they get it? Buying it on a device would be fine - perhaps even preferred.

This is for people in the UK, by the way.

And therein lies the problem.
It's not always so easy to obtain the software you want for a GPS unit the legal way.
Retail (software only) packages are few and far between...or do not exist at all.
If you buy a Garmin, TomTom, or Becker, you know what software you will get.
If you buy a new unit that runs a flavor of WinCE, it is not always clear what, if anything, comes on it.
Many seller sites will extoll the virtues of the included software ("Voice instructions!" "800 countries included!" "New maps!") without ever stating exactly what it is. This includes units sold on sites like DealExtreme, E-Bay, or even Amazon. Another example is/are units sold at Aldi. In Australia, a "Go Cruise" unit will generally come with Primo (Great!), in the UK and Europe, a Medion will come with Go-Pal (Cringe Worthy!). Same chain of stores, almost identical hardware, different offers.
So you have to do your own research and ask some very direct questions to the seller. If they will not disclose the exact software that comes on their unit, that may be a red flag as to whether you want to trust a purchase from them.
All this is among the reasons we here offer the services we do. Not just because it's fun to travel the seven seas with a patch on our eye, a parrot on our shoulder, singing "Ahoy there Matey..yo ho ho and a bottle of rum", but to help people obtain and use the best software for their GPS device. Which is maybe TOO HARD to get otherwise.