First stop is usually the Dali museum in Figueres, followed by his house in Port Lligat (Cadaques). This last has to be booked online and the museum ought to be also, to avoid queues. Added to these is the medieval Púbol Castle (near Flaça, and on the fantastic medieval villages cycle route), where Gala lived in the 1970's.
To this i would add 2 more 'sites'! Els Angels Mountain Sanctuary just outside Girona, again a popular cycle route, where the couple got married late in their relationship and last but not least, Can Manolo's Restaurant, in Girona, where they held their reception. Make sure you ask to be in the old part of the restaurant to get the full atmosphere (though the food is equally wonderful in the extension looking over the river).
While you're in Figueres you can visit the Sant Ferran Castle, where Dalí did his military service and Plaça de la Palmera where he had a second home. On leaving Figueres look for the Molí de la Torre, a property which belonged to the Pitxot family and where Dalí learned to paint.
Salvador Dalí - A Soft Self-portrait