I reecently listed an awesome older photo album on Ebay and the bidding heated up quick. I started it at 99 cents and as of this post its a few days into the auction and up to $41.00 already.
In any case what to look for? A nice old album itself is desirable (that holds the photos) and people like when they are identified ones. So if you see some older photos and you know who the people are (from the front or back of photos) those usually do better. Older photos like those shown in this blog post are what to look for. This is the Seymour family album some pictures which date back to the 1800s!