The Adventures of TomBombadil, which can be found in <i>Tales From The Perilous Realm</i> also has the barrow-wight:

"Dark came under Hill, Tom he lit a candle;
upstairs creaking went, turned the door-handle.
'Hoo, Tom Bombadil! Look what night has brought you!
I'm here behind the door. Now at last I've caught you!
You'd forgotten Barrow-wight dwelling in the old mound
up there on hill-top with the ring of stones around.
He's got loose again. Under earth he'll take you.
Poor Tom Bombadil, pale and cold he'll make you!'

'Go out! Shut the door, and never come back after!
Take away gleaming eyes, take your hollow laughter!
Go back to grassy mound, on your stony pillow
lay down your bony head, like Old Man Willow,
like young Goldberry, and badger-folk in burrow!
Go back to buried gold and forgotten sorrow!'

Out fled Barrow-wight through the window leaping,
through the yard, over the wall like a shadow sweeping,
up hill wailing went back to leaning stone-rings,
back under lonely mound, rattling his bone-rings."

<i>The Silmarillion</i> has some stuff about barrows in it too, telling the stories of how certain barrows were made - one was raised to cover the bodies of everyone killed in one particular battle (don't remember which, sorry!), another for the body of one of Turin Turambar's female relations (his sister? again, I can't remember properly).