With the plethora of mods out there, you've got several of them which have ways of producing Eu. The question here is... are they really worth it? These are simply my opinions, and others are free to chime in with their discoveries and/or opinions. Please keep it clean and flame-free, though.
Forestry has the Biomass Generator. Produces 8 eu/tic on biomass and twice that on biofuel. However, biofuel requires the Refinery, which takes up two diamond gears, so rather expensive, and eats up its own BC power requirements. Honestly, two biomass generators on biomass is probably going to be more cost efficient than one running on biofuel.
It's a novel concept, and biomass is a renewable resource (compost and saplings are what I use). Requires a bit more infrastructure than a regular Generator to get going, but that infrastructure can support several generators. I'd probably call it on par with a generator, but can't match the Geothermal.
Compact Solars is an addon for IC2, and pretty much is a space-saver. If you like Solars, you'll really like Compact Solars.
Transformers does what it says on the tin... converts BC MJ into IC2 Eu and vice versa. However, the conversion ratio does not favor Eu, and producing significant quantities of Eu with BC power doesn't seem very cost efficient. about 13 MJ for 32 Eu'Tic. That's roughly three Biogas Engines or Combustion Engines. You could also use a pair of Commercial Steam Engines with Railcraft, but that requires a whole infrastructure of its own.
Railcraft just came out with the Steam Turbine which produces a whopping 100 Eu/Tic! Only... there's a few problems. First, the turbine itself requires a massive 486 steel! It is also a 2x2x3 block megastructure, and requires about four separate gold waterproof pipes to keep it supplied with steam, and a fairly large boiler to produce that much steam. But wait... there's more! In addition to this enormous material investment in the infrastructure and in the bloody thing itself, you've also got a turbine rotor, that's another 33 steel, which slowly takes damage and eventually needs to be replaced! Now you're effectively burning steel for power. Not worth it, in my opinion. If you want to use steam for Eu, use about seven Commercial Steam Engines and hook them up to a MV Pnumatic Generator from Transformers for 128 Eu/Tic. Sure, you've got a massive investment in infrastructure, lots of steel and blaze powder and magma cream to get it going, but at least those are mostly one-time investments. Your only real ongoing costs is fuel for the boiler.