Craft is helpful. We used that a lot in our last campaign. There were nights when a good portion was spent making stuff. Arrows, sling bullets, swords, bows, alchemist fire, acid, pretty much anything you could want (except, sadly, siege devices that halfling died). We didn't even have to buy bottles, had the air gensai make some for us.
Spot, Listen, Move Silently, Hide, Bluff/Diplomacy/Intimidate and Sense Motive also tend to be helpful as well. I'm going to start investing in Climb, especially since my character enjoy heavy armor. Spellcraft is useful for the spell users, though generally not everyone else; however, Use Magic Device would be good for non-spellcasters. Escape Artist is helpful, even if you don't get caught a lot you can use it to escape grapples, though a typical fighter will have good BAB and Strength to do this anyways.
Really, it depends on the campaign and the most common occurances. But Spot and Listen would be two I'd put ranks regardless of if they're class skills or not.