These are fast loading and reliable for storing addresses, maps, music and POI.  You can put a lot of stuff on 512MB.
Fits many models including:

Garmin Colorado

Garmin iQue: 3200, 3600, M3, M5

Garmin Nuvi: 300, 310, 350, 360, 370, 660, 670, 680

Garmin StreetPilot: 7200, 7500, c310, c320, c330, c340, c530, c550, c580

Garmin Zumo

Harmon Kardon GPS-500

Magellan Maestro: 3100, 3140, 3200, 3210, 3220, 3250, 4000, 4040, 4050

Magellan RoadMate: 2000, 2200T, 2500T, 3000T, 3050T, 6000T

Magellan Triton: 1500, 2000, 400, 500

Navtour: NT-147

Nextar: Q3, W3, W3G

TomTom Go: 300, 500, 510, 520, 530, 720, 730, 920, 930

TomTom One V1