How to: Convert HTML form data to JavaScript Object using jQuery

serializeArray  already does exactly that, you just need to massage the data into your required format:

$.fn.serializeObject = function()
{
    var o = {};
    var a = this.serializeArray();
    $.each(a, function() {
        if (o[this.name] !== undefined) {
            if (!o[this.name].push) {
                o[this.name] = [o[this.name]];
            }
            o[this.name].push(this.value || '');
        } else {
            o[this.name] = this.value || '';
        }
    });
    return o;
};

Example of this in action:

HTML:

<h2>Form</h2>
<form action="" method="post">
  First Name:
  <input type="text" name="Fname" maxlength="12" size="12"/> <br/>

  Last Name:
  <input type="text" name="Lname" maxlength="36" size="12"/> <br/>

  Gender:<br/>
    Male:<input type="radio" name="gender" value="Male"/><br/>
    Female:<input type="radio" name="gender" value="Female"/><br/>

  Favorite Food:<br/>
    Steak:<input type="checkbox" name="food[]" value="Steak"/><br/>
    Pizza:<input type="checkbox" name="food[]" value="Pizza"/><br/>
    Chicken:<input type="checkbox" name="food[]" value="Chicken"/><br/>

  <textarea wrap="physical" cols="20" name="quote" rows="5">Enter your favorite quote!</textarea><br/>

  Select a Level of Education:<br/>
  <select name="education">
    <option value="Jr.High">Jr.High</option>
    <option value="HighSchool">HighSchool</option>
    <option value="College">College</option>
  </select><br/>

  Select your favorite time of day:<br/>
  <select size="3" name="TofD">
    <option value="Morning">Morning</option>
    <option value="Day">Day</option>
    <option value="Night">Night</option>
  </select>
  <p><input type="submit" /></p>
</form>

<h2>JSON</h2>
<pre id="result">
</pre>

JavaScript:

$.fn.serializeObject = function()
{
    var o = {};
    var a = this.serializeArray();
    $.each(a, function() {
        if (o[this.name] !== undefined) {
            if (!o[this.name].push) {
                o[this.name] = [o[this.name]];
            }
            o[this.name].push(this.value || '');
        } else {
            o[this.name] = this.value || '';
        }
    });
    return o;
};

$(function() {
    $('form').submit(function() {
        $('#result').text(JSON.stringify($('form').serializeObject()));
        return false;
    });
});

CSS:

form {
    line-height: 2em;
}
p {
    margin: 5px 0;
}
h2 {
    margin: 10px 0;
    font-size: 1.2em;
    font-weight: bold
}
#result {
    margin: 10px;
    background: #eee;
    padding: 10px;
    height: 40px;
    overflow: auto;
}