To be honest, I personally would hold off on Celebration lamps and wait for a better xp promotion to come. The max bonus xp yield on Celebration lamps is 10% right? I'm pretty sure Lava Lantern lamps can yield up to 150% and the Supremes; MadDrunk mentioned are 200%.
If you're targeting specific skills I would wait for Lava Lantern lamps or the Supremes like MadDrunk said. What CryingHawke mentioned is good too if you're not targeting specifics. _.•´¯`•._.•´¯`•.* D E L A Y *.•´¯`•._.•´¯`•._