inducible mammalian expression vectors

[rmoldwin at midway.uchicago.edu]

Can anyone suggest the a good inducible mammalian expression vector, with very 
tight control (i.e. not leaky).  We're trying LacSwitch now (Stratagene), but 
are considering one of the tetracycline operon plasmids.  Unfortunately, I can't 
seem to locate a plasmid that has both the repressor and the 
promoter/operator/insertion-site region on a single plasmid.  Does anyone know 
of such a vector, or have a better suggestion for an inducible vector?

It would be even better if the vector could multiply by episomal replication.

Thanks,
Rich