On my Tekkit server I have several solar arrays and a nuclear reactor producing tonnes of EU, and most of it if going into storage and rarely used en masse. Aside from a mass fabricator, how could I use this EU in a productive way?
That's about it: a mass fabricator. Anything less doesn't need all that power, since the draw is so low that it might as well be free. Even then, once you've made everything you want from UU matter, you'll still have more power lying around than you need to keep your godlike gear fully charged.
Though, if you have the EU to power a small town, maybe you could start using it like that. Build things like street lamps using Luminators just because you can waste the power on something so frivolous. The wiring and building challenge of a huge power grid (and the aesthetic structures to go with it) may be worthwhile all its own.
You could always try building Overclockers for your basic machines (Macerator, Compressor, Extractor ect.) to make them run faster, They also eat up a lot more power when they're overclocked so if you're wanting to burn off some EU that'd be the fastest way to do it.
Check the wiki for more info - http://thetekkit.wikia.com/wiki/Overclocker_Upgrade
Like the wiki also says you'll need to put in Transformer upgrades to actually deliver more power the machine quickly enough to get the most benefit - http://thetekkit.wikia.com/wiki/Transformer_Upgrade
And you'll also need to use Glass Fiber Cable to minimise the power loss across the duration of the cable - http://thetekkit.wikia.com/wiki/Glass_Fibre_Cable
That should help you burn off your EU a bit quicker :)