Not sure any of these players are great "buy and holds" as the race is far far from over. First Solar is just one of a handful that look like they're breaking the $1/watt milestone. Another promising one is http://nanosolar.com/

Then you have to look at how cheap natural gas will be over the long term - particularly given the new and massive abundance of shale gas. Gas in particular has the potential to push out adoption of solar. If there's one thing for certain, it's that coal fired power is going to be largely replaced - but the question is by what. Nevertheless, that firms are breaking the $1/watt barrier, is very good news for end users of power.