I may be moving from the US to the London for a job offer and I'd like my girlfriend to come with me. We would live there for a few years at least, so she'd like to find a job there. What options are available for this situation regarding visas? Should I tell my company about her, hoping they'll help? We don't want to get married, but have lived together for a while so I consider it a substantive relationship. We're both US citizens.
Since you are not married, she will have to get a general visitors visa. If your company is paying for housing/ relocation, I believe that you must tell them your situation. They are NOT LIKELY to help financially, but they may be able to give you some more information about the transition with a domestic partner.
I believe the visa will be good for up to six months, but during her stay, she will NOT be able to work there.