A regular TileLayer with grayscale makeover.
Just use L.tileLayer.grayscale(url, options)
instead of L.tileLayer(url, options)
.
http://zverik.github.com/leaflet-grayscale/
This plugin was written by Ilya Zverev and published under WTFPL license.
TileLayer.WMS converted to grayscale. Same extensibility created for conventional raster tiles applied to the WMS tiles.