Soldering Iron....

For me, smaller is always better. I'd get something like this if I didn't want to spend too much. If I need to do something bigger like battery terminal connectors, a small butane torch works just fine.

[ame="http://www.ebay.com/itm/Weller-WES50-Soldering-Station-/171276110509?pt=LH_DefaultDomain_0&hash=item27e0da0aad"]Weller WES50 Soldering Station | eBay[/ame]