Tiger Lily became Ultravox! and then dropped the exclamation mark after the second album.

Quite a few bands shortened their names:

Ambrose Slade > Slade
Arabacus Pulp > Pulp
Southern Death Cult > Death Cult > The Cult
Easy Cure > The Cure

Simple Minds - Johnny And The Self-Abusers

Bellefire were originally called Chit Chat

Madness used to be Morris and The Minors, then The Invaders.

'Marilyn Manson' were originally called 'Marilyn Manson and The Spooky Kids'.

It fitted in with the zany cartoonish style at the start but would have seemed rather silly later.

I was going to say Joy Division, but Warsaw isn't that bad is it?!

Weren't Travis originally called Glass Onion or something?

The High Numbers --> the Who
The Ravens --> the Kinks
The New Yardbirds --> Led Zeppelin
The Rollin' Stones --> the Rolling Stones
Traffic Jam --> Status Quo

The Beatles had lots:
- Johnny and the Moondogs
- Long John and the Silver Beetles
- the Silver Beatles

The Sex Pistols started out as 'The Strand' (when it was Jones, Cook, Matlock and Nightingale), but only performed one gig under this name. They changed to 'The Swankers' but did no gigs. Then they become 'Kutie Jones and his Sex Pistols'. When Nightingale left and Jones moved to guitar, and Rotten came in on vocals, the Kutie Jones bit was dropped, hence 'The Sex Pistols'.

The Eurythmics were The Tourists weren't they?

Not exactly, Annie Lennox and Dave Stewart were in the band The Tourists, but left to form The Eurythmics

The Lotus Eaters > Cherry Keane > Keane

Tragic Love Company > Stereophonics