There's Lemon Verbena, and a Pelargonium with lemon-scented leaves. Can't bring to mind any others at the moment...

There are some lemon thymes

Lemon: balm, basil, mint, thyme, golden thyme, lemon scented catmint (which cats don't like!) and lemon grass

I have a geranium that smells of lemon serbet. It make your mouth water when smelt or touched. My hubby puts the dry leaves in the car ash tray as an air freshener.