http://wordpress.org/extend/plugins/relevanssi/
This plugin improves WordPress’s default search functionality. By default, WordPress sorts the search results by date, rather than by relevance. Relevanssi is much smarter, and allow for a smart search on your post.

http://sparepencil.com/portfolio/advanced-excerpt/
This adds to WordPress’s excerpt functionality: Mainly, you can use html in the excerpt.

http://contactform7.com/
This is quite possibly the best contact form plugin out there. If you need a simple, customizable contact page, this will undoubtedly be what you need.

http://www.viper007bond.com/wordpress-plugins/syntaxhighlighter/
At a guess, I’d say that almost all of us knows what Alex Gorbatchev’s syntax highlighting jquery plugin is. It allows for super-simple code highlighting, and this plugin adds that functionality to WordPress.

http://aahacreative.com/our-projects/tabs-wordpress-post-editor/
This is used in conjunction with the SyntaxHighlighter Evolved plugin above. It allows tabs in the post editor, which makes writing code much easier.

http://kingdesk.com/projects/wp-typography/
This adds some great typhography features to your site. For example, it automatically adjusts the quotes in wordpress to be “right” and “left” quotes, instead of just straight up. It also replaces subtraction signs with hyphens. Take a look at their site for a full list.

http://urbangiraffe.com/plugins/headspace2/
This makes your posts much more SEO-friendly. Mainly, it allows you to add separate meta information to every one of your posts.

http://ocaoimh.ie/wp-super-cache/
This is exactly what its title says: It caches your site, which significantly decreases page load time.

Now, to the tutorial.

First, go to your theme’s index page and make a div that will hold the new post.

<div id="post"></div>

Still in your index page, go to your post loop section and add this code to your post links.

rel="<?php the_ID(); ?>"

This isn’t that important, but it does give us extra information if we ever need it.

It doesn’t matter where this div goes, as long as it is somewhere on the index page. Once you have the div in your theme’s index.php file, go to your single template and delete everything except for the post itself – this is what will display in our “post” div. It should look something like this:

<div id="post_container">
	<h1 id="post_header"><a href=""><?php the_title(); ?></a></h1>
	<div id="post_date"><?php the_time('l, F jS, Y') ?></div>
	<div id="post_text"><?php the_content(); ?></div>
</div>

Now, go into your header.php file and write this code in a script tag.

$(document).ready(function(){
	$.ajaxSetup({cache:false});
	$("a").click(function(){
		var post_url = $(this).attr("href");
		var post_id = $(this).attr("rel");

		$("#post").html("loading...");

    $("#post").load(post_url);

window.location.hash = post_id;

return false;
	});
});

Now, step by step:
1.When the document is ready, set jquery’s cache to false.
2.Then, add an click event handler to every link on the page. Change the “a” to wherever your post links are.
3.Put the text “loading” into the post div.
4.Load the post into the post div.
5.Set the url to show the post id, change this to whatever you want.
6.Make the link not actually work.