I have a customer that wants an exhaust fan mounted directly above the shower stall. I can't find any codes that forbid this. This is a remodel in a small bath and there really isn't anywhere else to go with it.
Any thoughts welcome here.

There are several exhaust fans that are listed for use in shower stalls. The ones I've seen have a label inside the rough housing that will says-"Suitable for use in a shower or over a tub when installed on a GFCI protected circuit" or words to that effect. I know that Broan and Nutone make one for sure.

The code in question would be 110.3(B)

You would need to use a product listed for this location.

The following is excerpted from UL's White Book section on Fans, Electric (GPWV)

"Ceiling-insert fans, wall-insert fans, and ceiling-insert fan/light combinations intended to be mounted over bathtubs, showers, or within the zone above the bathtub and shower area as defined by Article 410 of the NEC, are marked "Acceptable for use over a bathtub or shower when installed in a GFCI protected branch circuit." These products are investigated to determine the effects of moisture (dampness or wetting), such as shower spray."

You can find the entire text of (GPWV) at
http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?&name=GPWV.GuideInfo&ccnshorttitle=Fans,+Electric&objid=1074009331&cfgid=1073741824&version=versionless&parent_id=1073987360&sequence=1

We use a lot of Panasonic fans over the shower and tub on a GFCI protected circuit. The smaller fans are rated at 0.3 sones. Extremely quiet.