Initially, most bee species will provide some type of comb that will produce Beeswax and Honey.
Beeswax is a generally useful thing, being able to make Pipe Waterproofing with it is good enough, but then you've also got Wax Capsules you can make out of it, which can give you a fully renewable way to mass-produce things like Bog Earth
Now, Honey by itself can be used to produce Honeyed Slices, which are an amazing food source. However, put it in a squeezer, and you get Liquid Honey, with a chance of Propolis. Now, Propolis is a generally useful thing, you can make apiarist's pipes with 'em, for example. It can also be Centrifuged into Sticky Resin. I think any purveyor of IC2 knows what to do with that. Generally, you're already going to have rubber trees, but if you get stuck in a bad spot without any rubber trees nearby, it can be quite useful to get yourself going.
This is all from the basic bees you find lying around the world. Bee Breeding can net you some truly amazing species with some very interesting drops.