GPS File Depot is a great site for Garmin-ites. The maps on there are excellent quality, and they usually have several choices for each state based on what you're looking for. I have a 1GB microSD in my Oregon (in addition to the 1GB on-board storage) and keep hi-res topos of SoCal (full Cal is too big), AZ, NM, and CO on it at all times Each map is around 200-300MB I think.