The best/easiest way is to probably find a fund which chooses only socially responsible investments. A site like http://www.socialinvest.org/ would probably be helpful.
There aren’t really any large socially responsible companies (IMHO) and even many of the promising ethanol companies have major shareholders from Big Oil. If you were thinking investing directly in a small company, it is a little trickier.
Having founded a green biotech company, I can certainly tell you there are many more companies than you ever imagined. However, direct investment in many of the “green” companies, because most are small startups, require >$10,000. They are effectively looking for Angel Investors to get the company off the ground and the idea generating some data. There are Angel Investor groups around the country which parade the potential investment companies before the investors. Many of these angel groups have a green or responsible focus. Usually a company is trying to raise $250,000-$1,000,000 which is why the smallest investment accepted is >$10,000.
As far as finding out about promising technologies, the internet is your friend. Local companies are always trying to get in the press with government grants earned or the affiliation with a local university. Technology Transfer offices are ubiquitous at most universities now and they will also list recent companies coming out of the university’s research and technology.