Daniel Schweinert builds custom 35mm depth of field (DOF) adapters for cameras and camcorders that allow you to use traditional 35mm lens on your camcorder. While he sells many of the kit parts himself, he puts all of the instructions online for free, should you want to try your hand at building your own. I browsed through the instructions for building an adapter for the HV20 last night, as pictured here, but it's a bit more money than I want to throw at it yet, especially since I'm just now learning the camera. Still, it's far cheaper than commercial 35mm adapters, which can run from the high hundreds into the low thousands.
Why would you want to do such a thing? For one, it turns your little camera into a black-and-silver monstrosity mounted on a sled so that you don't rip out the plastic lens threads. (I think that's neat. You may not.) It also can help you to produce really pretty footage with great depth of field and lots of bokeh. The footage below is shot with a commercial adapter, the Letus35 Flip, and a Panasonic DVX100a, a 3 CCD camcorder, but should give you a good idea of the general effect.
Daniel's GG-Holders Tutorials [JetSetModels.com via Eugenia]