Another idea - since the LICH is immune to poison and disease..what about stocking the lich's lair with yellow mold and every other kind of toxic subtance which the players will be forced to step on, breathe etc....
Brutally brilliant!
I could even see it letting itself become a "carrier" of a lethal mold or 2, adding to its fearsomeness.
Player: "Why does that lich look like its wearing a puffy patchwork yellow, brown and green sweater ?"
DM: "Bad tailor, perhaps? Heh, heh, heh..."
Or Wu Jen Lich, or Beguiller Lich. A Warlock Lich would be easier to run, but significanly less powerful.
A Bard Lich would be weird.
Alternative builds can be quite dismaying to the party...
I did one that was a SpecWiz Necro/Shaman (OA) who, among other things, relied more heavily upon touch-attack spells...which he delivered with his Unarmed Strikes. This meant that those it struck had to deal with 1) the spell effect, 2) the unarmed strike damage (boosted by 1d8+5 by the Lich's negative energy channeling), and 3) the lich's Paralyzing Touch.
(And had I coupled all that with wearing mold as suggested above...)
A BttlSorc or WarMage Lich could also be a bit of a rude surprise, standing there in its magical Mithril Plate (having taken the Battle Caster feat). They may even think its a Deathknight...
I can't say I've ever done a Bard Lich, but I have done a Bard Vampire. I know, kind of cliche.