Recommended Soldering Iron

My son wants to build his first headphone amp (kit). He's asking for a soldering iron for Christmas. Can anyone offer up some information on what I should be looking for? He wants to start off with one of those Altoid can amps and work up to tube. I don't want to go too cheap but rather a decent one he can sell if he loses interest. He's 19 so we don't need the Easy Bake Iron. Any information is greatly appreciated.