Nokia N8 comes with pre-installed OVI Maps for navigation using GPS. The OVI maps are free to use on Nokia N8 and work in accordance with GPS functionality. There is another post in this blog which talks about updating the OVI application and downloading the OVI maps for the selected country on your Nokia N8 mobile.
Yes there are other free GPS applications available out there which you can install on your Nokia N8 mobile. The First one is Google Mobile Maps which ofcourse uses google maps for navigation. The Google Mobile Maps application can be downloaded from OVI store or from official google website for google mobile maps. On the official google mobile maps website you can even enter your mobile number and google will send you an sms describing how to download the free GPS application and install it. The Google Maps GPS application will require internet access using GPRS to provide you maps and provide GPS navigation.
There is another free GPS application which you can download on your Nokia N8 mobile and use it to navigate Yahoo Maps, Google Maps, Windows LIVE maps and even Open Street maps. The free GPS application is named as Mobile GMaps. This free GPS application can be downloaded from official website of Mobile GMaps and requires Java support. The Nokia N8 allows Java application to be run and hence you can easily download and run the Mobile GMaps application and use it for free.