I am looking for a good GPS/maps app for the N900 with the following features: (in order of how important they are to me)
1.Has good reliable maps of Australia (specifically Perth)
2.Doesn't download huge amounts of data over 3G when in use. Being able to download/cache some/all of the Perth area locally would be nice but not essential.
3.Can support Google GTFS data feeds for public transport (my local public transport operator makes such data available) so I can use it to find stops near where I am, find out what services leave from those stops and where they go etc. Trip planning would be great if it was possible.
4.Lets me set my destination and can tell me when I am approaching it (so e.g. I know when to get off the bus)
and 5.Has route planning for walking that can find the shortest way (in distance terms) to walk from where I am to where I want to be including telling me how long (in distance terms) that journey is.

Nokia Maps supports #1 and #2 great but it doesn't do #3 so its useless to me for the purpose.
I dont need turn-by-turn or voice guidance as I am not driving a car. (dont even own one or have a license)

AFAIK requirement 3 is not fulfilled by Modrana, Yosmapa, Marble or CloudGPS. These are the most developed recent apps.

Have a look at Mappero and ModRana. I am not sure if they will satisfy all your requirements, but I depend on them (more on ModRana) when I plan oversea road trips. As both will cache maps for offline used, they worked very well for me as long I stay within the planned path (if I don't have access internet). The work around is to pre-download a larger area of the offline maps before you take off for the trip. And you have a rather large list of open maps to choose from (including Google maps).

I think #3 is really what I need in order for it to be worth replacing Nokia Maps.