Touratech also sells one that does not require guards for attachment. Pricey but probably of very high quality, as are most Touratech products (I haven't seen this one).
I've tried both the Givi and SW Motech skidplates. The Givi is made of very thin, lightweight aluminum and certainly won't take skidding over rocks, logs, etc., but does well for protecting the oil filter from flying rocks, etc. The SW Motech is made of substantially thicker aluminum but has two wings (for lack of a better word) that are riveted to the center piece. After some really heavy bashing (high centering 3 times on the plate and a couple of drops) about half of the rivets broke. That's easily fixed and it did fulfill it's intended purpose, protecting the engine, oil filter, etc., and could still be ridden home.
I don't know of any other skidplates that don't attach to the guards than those already listed. I don't think any of these are up to the standards of true dirt bike bash plates but should work well for lighter duty use.