How much power do you need to handle? Gralab 300 will handle things but I
think it only handles up to 600 watts. Used not that much money. New might
be cheaper to get a new popper -)

Nick

Gralab 300 should work just fine

Plenty of these on eBay

Cheapest solution:
http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?xi=xi&ItemId=161159
9133&ccitem=

or google "spring wound timer"

There are lots of timers like this available.  The only caveat is to
check the amperage rating of the timer and the current requirement
of your popper.  The current rating will be stamped on the timer.  
Many of these timers are still in production and the manufacturer's
web page should have the specifications.

ebay is the place to look, although a wtb advert on
rec.photo.marketplace.darkroom should bring a response.

If you are bottom feeding then try, for instance:
   ebay item 7592752578
             7594502902

Search for 'Mark Time' - they are the cheapest on the market.
Most are 60 second timers, but some are 10/30/60 minute units.
Don't pay much over $4.99 for one.  Repeatability on these isn't
going to be much better than +/- 15 seconds.

Next are the GraLab and Time-O-Lite: both are very nice timers
just to have around the house.  Prices are $5 to $60 and vary
for no apparent reason.  Either of these is good to better
than +/- 1 second.

   ebay 7592812846
        7593236351

Many of the Time-O-Lite's have a 'repeat' feature where you just press a
button to get the same time again.

As suggested, try Grainger and McMaster-Carr - but be
prepared to spend a lot more money.

Gralab 300, 168, 171, 167 all time various intervals.  All available from
that auction site.  Features vary per model, I use them in my kitchen as
well as in the darkroom.