Most of our clients and other companies I discuss this with are too concerned with giving any indication of actual qty available, they basically don't want that information available for their competition.
Give a competitor the opportunity to build a script to beat on your site in order to figure out how much inventory is available and they'll do it - we once had a competitor hit our clients site and suck down pricing info with a script to help them determine pricing for their upcoming master catalog. We decided to intercept their requests and feed them pricing that was 5 to 20% higher :)
Anyway, what our clients have done is simply display when the items will ship. For instance, some of our clients have a policy that all orders ship same day (M-F) if the order is received by 2pm their time. Assuming the item is in stock. After 2pm the web site toggles to either indicate the item will ship in 24 hours or if it is Friday, the item will ship on whatever date that following Monday is.
If there are no items in stock but we have a purchase order date, then we display that date as the next available product ship date. Of course this entire process only works if you have real time communication between your back end piece and the eCommerce system; which they do.
Some of our clients will toggle the availability of the items to indicate something to the effect of "low qty available" and actually find that doing so drives sales. One company I recently talked to said they even did that when the qty wasn't low just to see if it would impact sales; noticeable increase in orders placed.
I would of course advise against doing this as a regular practice since it could back fire if it ever became known by your customers.
Hope that helps.