I assume you're asking for the full HTML string. If that's the case, something like this will do the trick:

$('<div>').append($('#item-of-interest').clone()).html(); 

This is explained in more depth here, but essentially you make a new node to wrap the item of interest, do the manipulations, remove it, and grab the HTML.

If you're just after a string representation, then go with new String(obj).

Update

I wrote the original answer in 2009. As of 2014, most major browsers now support outerHTML as a native property (see, for example, Firefox and Internet Explorer), so you can do:

$('#item-of-interest').prop('outerHTML');

Just use .get(0) to grab the native element, and get its outerHTML property:

var $elem = $('<a href="#">Some element</a>');
console.log("HTML is: " + $elem.get(0).outerHTML);

Can you be a little more specific? If you're trying to get the HTML inside of a tag you can do something like this:

HTML snippet:

<p><b>This is some text</b></p>

jQuery:

var txt = $('p').html(); // Value of text is <b>This is some text</b>

new String(myobj)

If you want to serialize the whole object to string, use JSON.