PTLens is now advertising itself as an external editor for Lightroom. While not in the same form a plugin would take, it’s still quite similar to some Aperture plugins, i.e. convert the file and process it then.
For those not familiar with PTLens, it provides lens distortion corrections not currently available in Lightroom. To be precise it fixes pincushion/barrel distortion, vignetting, chromatic aberration, and perspective distortion. The corrections are automatic based on a database of lenses.
There is a trial version available, which can be converted to a full version for a paltry $15. Note that the external editor requires V2 of Lightroom.