I think I need a little more context. Can you tell me what the company is, and what they do? Do they prefer something more formal, like an insurance company or financing, or are they casual like a restaurant or a dotcommer?

-Andrew Welfle

Can't tell you a whole lot / understanding you need a context > client is a (large) fashion retailer, target group women.

In proposals trebuchet was used, but i'm looking for something a little bit sleeker (thinner).

Thnx

Meta is pretty close to Trebuchet and is a nice typeface.

Right, Meta. Or maybe Syntax?

Trebuchet is very much an individual style. It is hard to match it up to another sanserif-style font. But if you are determined, try Gill Sans Light. It is of the artdeco style and might be what you are looking for. But, it only works mildly with Trebuchet Bold as long as it is of a smaller, lighter type size. It is not perfect, but works to some degree.

Personally, I would suggest a different type style for the fashion font. Two sans-like fonts don't always work well together. I would prefer a beutiful sans as the head, and a light, elegant serif as the tail.