Initial answer from 2013

An excellent (unofficial) Bootstrap Switch is available.

<input type="checkbox" name="my-checkbox" checked>
$("[name="my-checkbox"]").bootstrapSwitch();

It uses radio types or checkboxes as switches. A type attribute has been added since V.1.8.

Source code is available on Github.

Note from 2018

I would not recommend to use those kind of old Switch buttons now, as they always seemed to suffer of usability issues as pointed by many people.

Please consider having a look at modern Switches like this one from the React Component framework (not Bootstrap related, but can be integrated in Bootstrap grid and UI though).

Other implementations exist for Angular, View or jQuery.

import '../assets/index.less'
import React from 'react'
import ReactDOM from 'react-dom'
import Switch from 'rc-switch'

class Switcher extends React.Component {
  state = {
    disabled: false,
  }

  toggle = () => {
    this.setState({
      disabled: !this.state.disabled,
    })
  }

  render() {
    return (
      <div style={{ margin: 20 }}>
        <Switch
          disabled={this.state.disabled}
          checkedChildren={'开'}
          unCheckedChildren={'关'}
        />
        </div>
      </div>
    )
  }
}

ReactDOM.render(<Switcher />, document.getElementById('__react-content'))

Native Bootstrap Switches

See ohkts11’s answer below about the native Bootstrap switches.