History.

• <bgsound src="ghostbusters.mid" autostart="true" loop="999"> (IE)
• <embed src="sound.wav" volume="50" controls="console">
• <object type="audio/x-wav" data="test.wav"></object> (IE)
• navigator.plugins['LiveAudio']['audio/wav'] (Netscape)
• Flash .SWF + linked/embedded sound (made using IDE)
• Java Applets, Quicktime etc.

Present.

• 100% Flash-based audio (SWF object/embed)
• HTML5 Audio() / <audio> (still early, but there's that iPad thing etc.)
• SoundManager 2: JS + Flash Hybrid API

  soundManager.createSound({
    id: 'mySound',
    url: '/path/to/an.mp3'
  }).play();

SoundManager 2

• Reliable, cross-browser, cross-platform sound control via JS + Flash
• JavaScript API for MP3 + MP4/AAC audio, hidden Flash abstraction, API core as small as 9KB w/gzip
• Latest dev branch: Experimental HTML5 support, Flash fallback, seamless API, works on iPad

Show me the shiny.

• schillmania.com/projects/soundmanager2/
• waveform/spectrum data visualization (Canvas, data via Flash 9)
  

The Future?

• HTML5 implementations in flux, varying support/consistency (no single common format across all browsers.)
• HTML5 audio + video (pending issues: inconsistent format support, $$$/copyright/IP)
• H.264: "Technically superior, legally inferior" (+more expensive in 2016?)
• <audio> should be as easy as <img> - complicated copyright intrests means: It isn't. :/
• Mozilla Audio Data API (draft recommendation) - very promising