You could start on solar panels if you've only got a few machines or want a totally maintenance free form of power generation, but they could get quite expensive depending on how much power you are using (a metal former would take 10 to run non-stop on it's own for example, although if you've got something like a CESU storing the EU while you're not using it then that might not matter). The best options would be the kinetic wind/water generators, as they'll output a fair amount of power (at Y160 and a carbon rotor a few hundred EU is almost guaranteed with a kinetic wind generator) and are really only out-produced by nuclear reactors or steam setups.
i'd recommend kinetic wind/water generators for the beginning and maybe 20-ish solar panels if the wind gets calmer and later on get a small nukelear reactor like me that is outputting 100eu/t or maybe get the advanced generators mod and start making biogas.
I am going to recommend that if you use buildcraft or any mod that allows you to easily move fluids, to set up a fermentor on a liquid heat generator to a tank, then pipe the output (from the other side of the tank) to liquid heat generators and stirling generators. as long as you have plant material, you have a slow but steady power supply.
I run reactors but use this as my "diesel" backup.
If you don't have piping mods, a windmill with an iron rotor or two will hold you until you get a sustainable reactor built.
pipe the output (from the other side of the tank) to liquid heat generators and stirling generators
One note in terms of actual power generation a semifluid generator produces just as much power, just as quickly as a fluid heat-stirling generator setup does but only uses half the space. Might be intentional, might not be, but as far as I can tell that's how it is right now.
