1) The Bay Area (Silicon Valley + SF etc.) - Pretty much perpetually
2) NYC
3) Austin,Tx and Boston are tied
3.5) Chicago
4) Seattle, Boulder,Co ; and Los Angeles are tied
5) Any other major city with a good engineering school in the vicinity or other major money industry with that needs a few Computer Science and/or IT guys around (i.e. Oil)
A few cities like this include: Atlanta, Houston, Dallas, Washington D.C., Miami, Kansas City (especially since Google Fiber is rolling out there), and Las Vegas
Just for info, I currently live in Austin. Almost moved to SF but just finished school and prefer the nightlife in Austin