I am in the process of upgrading from EE1 to EE2. My EE1 site makes use of the SL Google Maps add-on, which does not seem to have an EE2 version. How do I handle this problem? Is there an add-on available for EE2 which allow me to upgrade relatively seamlessly?
We've ported SL Google Maps to EE 2 by ourself, but ultimately switched to Google Maps for ExpressionEngine from Objective HTML nonetheless after a few month of operating SL GM on EE2 and several Maps-API-changes made by Google.
I would recommend you to switch to Objective HTMLs Module too.
The big daddy of googlemaps add-ons for EE2 is http://devot-ee.com/add-ons/google-maps but afaik there's no seamless upgrade path. You could contact objective html and ask though.
Another Maps plugin I can easily recommend is Gmaps - the developer is always updating it and keep improving the experience..