Comment by munk-a

Cisco, Level3 and WorldCom all saw astronomical valuation spikes during the dotcom bubble and all three saw their stock prices and actual business prospects collapse in the aftermath of it.

Perhaps the most famous implosion of all was AOL who merged (sort of) with TimeWarner gaining the lion's share of control through market cap balancing. AOL fell so destructively that it nearly wiped out all the value of the actual hard assets that TW controlled pre-merger.