There's a few serious watch collectors on this board who can chime in on this. I'm not so sure I can consider myself an avid watch collector, but I've collected a few watches over the years.

Here are some of my thoughts:

Don't buy a watch based on a pretermined price ceiling (i.e. $900). Instead buy the watch you really and truly want, even if it means waiting longer and spending more money.

If resale is important, buy an automatic as opposed to a quartz.

Don't buy watches based on fashion, but do buy watches based on complexity. Automatic chronographs are especially valued; collectors see and measure the value of chronos similar to that of cars. For instance, a 1970's vintage Heuer Autavia watch powered by a Valjoux 7750 3 dial chronometer automatic is akin to a vintage Porsche 911S. The Autavia sold new for $100 back then. A well-maintained and working Heuer Autavia now goes for $2000-$3000.

Motorsports related and chronographs are great watches to buy, from a dress standpoint, as well as from a collectability perspective.

A couple of watch forums:
http://www.timezone.com/
http://forums.watchuseek.com/

A couple of articles regarding watch collecting:
http://forums.watchuseek.com/showthread.php?t=152
http://www.pmwf.com/Forum/JeremyKell...ctorsGuide.htm
http://www.time4watches.com/2.%20Wat...%20a%20Pig.htm

Hope this helps.