It's called the corporate we and it's fine to use! You might be a one-person company but really there's always at least two people: the natural person (you) and the juridical person (the company), hence "we".[0]

[0] http://en.wikipedia.org/wiki/Legal_personality

I can imagine some clients would find it disingenuous to have a company name when it's just you, yeah.

This post was interesting because my current boss had the exact opposite experience. He said when he dropped the "company/we" terminology he had been using and was upfront about how it's just him, his relationship with clients improved greatly. It probably all depends on the types of clients you have.

Just be honest. In my case I tell them I'm currently the only full time employee but expect to grow over the next 12 months, but that doesn't have to be the case. I admit I sometimes feel like Smeagol when I use the term "we", but ultimately it helps preserve the delineation between the company entity and myself as its employee.