Newer lead-free solders have been getting better and better. We recommend this SAC305, no clean flux core, solder for your projects!
We were great fans of Multicore Hydro-X leaded solder, but lead-solder's day has come and gone. Industry has since moved over to safer lead-free solutions such as 0.032" AIM SAC305 Solder that we now sell and use at Solarbotics.
Sold in convenient 6' lengths, this lead-free solder consists of 96.5 % Tin (Sn), 3% Silver (Au), and 0.5% Copper (Cu), with a melting temperature of 217° -218°C (423° -424°F) with a No clean Flux core. The No clean Flux is convenient because you don't have to clean up the flux residue if you don't want to as it is non-conductive and non-corrosive.
If you have a variable temperature soldering iron 725-750°F is a good setting to be at when using this solder.