Make sure that your scanner is compatible with 
your operating system, ESPECIALLY if it's 
Windows XP.  In my case, XP did NOT use the 
original software of the scanner but instead 
TOOK OVER the scanner with a less-capable (and 
faulty) software of its own.

The XP Scanner & Camera Wizard removes a lot of 
the features and functions from some scanners, 
and you can't do anything about it.  Make sure 
you can find a scanner that either works very 
well with XP (if you have it or ever think about 
upgrading to it) or can bypass that stupid 
wizard (which Microsoft makes it VERY difficult 
to do).

Besides that, I'll recommend that you find a 
scanner with a large scanning area, especially 
if you have oversized cels.

Alternatively, I would even think that a good 
digital camera would be a nice choice.  It can 
handle any-sized cel, the quality often turns 
out to be just as nice (when the photo is taken 
right), and you can grab a lot more use out of 
it compared to a scanner.