How do you convert a jQuery object into a string?

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');

With jQuery 1.6, this seems to be a more elegant solution:

$('#element-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);