The classic 'third hand tool,' as seen on every desk! We have one next to our Panavise jr, they complement each other well. This tool is good for holding small PCBs and wires for tinning or soldering to parts.
Even though there are fancier ones with soldering-iron holders, we found those would constantly tip over when a soldering iron was in place so we suggest getting one of these and a separate soldering iron holder/stand.