For now, even the 'stable' portal version is giving errors from time to time. Reloading the page should fix it.
The portal for the external users is at http://portal.vamdc.eu/vamdc-portal-stable/. At this time, this portal supports only spectroscopic databases; collision and reaction queries are not working. A better portal will replace this one in February 2012.
The portal for VAMDC's internal testing is at http://portal.vamdc.eu/vamdc-portal-test/. This is only for VAMDC developers; you need a password to get in.
The "level-2 portal is no longer available (use the "stable" one, above).