$-cache-with-find.js

function Selector_Cache() {
	var elementCache = {};

	var get_from_cache = function( selector, $ctxt, reset ) {

		if ( 'boolean' === typeof $ctxt ) { reset = $ctxt; }
		var cacheKey = $ctxt ? $ctxt.selector + ' ' + selector : selector;

		if ( undefined === elementCache[ cacheKey ] || reset ) {
			elementCache[ cacheKey ] = $ctxt ? $ctxt.find( selector ) : jQuery( selector );
		}

		return elementCache[ cacheKey ];
	};

	return get_from_cache;
}

var cache = new Selector_Cache();

// get selector
cache( '#selector' );

// get selector and reset cache
cache( '#selector', true );

// get selector with $ctxt
cache( 'img', cache( '#selector' ) );

// get selector with $ctxt, and reset
cache( 'img', cache( '#selector' ), true );

// get selector with $ctxt, and reset both selector and $ctxt (whoa)
cache( 'img', cache( '#selector', true ), true );