Tomtom are offering an extra 6 months (2 extra maps) when you purchase the map update service before the end of March.
I think it's an ok deal especially if you travel and use your sat-nav a lot.
It depends on what maps you have but connect your device to TomTom Home 2 and it will give you a personalised price.
I have a current UK & Ireland map and it is quoting me £27.80 (Tomtom GO 520)
From Tomtom website "Throughout March you can get an additional 6 months from our map update service. You can pay for 12 months and use the service for 18 months, which means you get 2 extra map updates for FREE."