The craft beer bar behind the north stand last season was good. I think it was called the Greene King academy or something. I don't normally like modern IPAs as they are too citrusy / fruity / hoppy, but these were nice, and much better kept than the ales in the Kings cask bar. I haven't been to the Quins Head now.
It does seem a shame that they can't team up with Fullers, being a local brewery of sufficient size to meet the likely demand (and much nice than Twickenham Ales) but I guess the numbers don't stack up