Free Icons: 'Silk' (see info for licensing details)

layers	layout	layout add	layout content	layout delete	layout edit
layout error	layout header	layout link	layout sidebar	lightbulb	lightbulb add
lightbulb delete	lightbulb off	lightning	lightning add	lightning delete	lightning go
link	link add	link break	link delete	link edit	link error
link go	lock	lock add	lock break	lock delete	lock edit
lock go	lock open	lorry	lorry add	lorry delete	lorry error
lorry flatbed	lorry go	lorry link