SQL Server "Suspect" database?
First thing is to make sure you DO NOT detach that database.

Restoring from the last known goodbackup is fine. Otherwise you will need to use the EMERGENCY repair mode (I am assuming you are running SQL 2005 or higher). Here are a couple of posts from Paul Randal on the subject. Read them both before you start taking any action.

Creating, detaching, re-attaching, and fixing a SUSPECT database

EMERGENCY-mode repair: the very, very last resort