To be honest most of the bands I saw beginning with 'L' have been pretty unmemorable to date. Obviously there are exceptions (the utterly amazing 'Levellers' and 'Lacune Coil' for instance) but most of them I can't remember well, if at all.

La Costa Rosa
Lacuna Coil
Laika
Larrikin
La's, The
Last Dance, The (2)
Laughterland (3)
Le Faye
Leechwoman (2)
Legend
Levellers, The (5)
Levitation (2)
Lick
Life of Agony
Lightning Seeds
Lilac Time (2)
Little Angels (2)
Little Barrie
Live (3)
Lobsterphone
Lo-Fidelity Allstars
London After Midnight (2)
Longpigs (2)
Looking Glass, The
Loop Guru
Lovebomb
Loverboy
Luxx