1. AdSense-Deluxe WordPress
AdSense-Deluxe is a WordPress plugin offering advanced options for managing the automatic insertion of Google AdSense or Yahoo Publisher Network (YPN) ads to your WordPress posts.

Adsense Deluxe WP Plugin

2. Adrotator
Ad Rotating Solution for your Ads. I think this simply sums up what you need to know.

Adrotator Plugin

3. Buy Me a Beer
This WordPress plugin allows your readers to donate money to you via PayPal. The plugin is widget enabled.

PayPal Donation WordPress Plugin

4. BankRollin
The only sure way to avoid being detected by Google for paid links is through contextual links. I am sure you have heard of this by now, you can download the free version which requires a link back to the site otherwise, get it for an affordable price.

WP BankRoll Plugin

1. Akismet
Checks your comments against the Akismet web service to see if they are spam or not. One of the best in the list.

Akismet SK Download

2. Spam Karma
Spam Karma is a great free replacement for Askimet. If you like to be different from the rest, try this.

Spam Karma Download

3. Contact Form Spam Killer
Spamming is going to happen everywhere and that is where this little plugin will help clear those trying to play punk in your contact form.

WP Contact Form with Spam Protection | Download Direct

4. Defensio
In order to use this effectively, you should deactivate Akismet and/or any other anti-spam plugins before using this.

Defend against spammers Download

5. Simple Trackback
Simple Trackback Validation Plugin for WordPress 2.x performs simple but very effective tests on all incoming trackbacks in order to stop trackback spam.

Simple Trackback Validation Plugin

1. WordPress Database Backup
It allows for one-click backups via download, server directory, or email, all straight from your WordPress administration interface.

WP Database Backup Download

2. WP-Cache 2.0
It works by caching WP pages and storing them in a static file for serving future requests directly from the file rather than loading and compiling the whole PHP code and then building the page from the database.

WP-Cache Plugin

3. Uberdose SEO
This plugin is streamlined for some best practices for Wordpress SEO. All in One SEO to tweak the default options.

All In One SEO Pack

4. Quick META Keywords
The Quick META Keywords Wordpress Plugin will automatically add META Keywords tags to every single post on your wordpress blog. Sounds Crazy, but it works well!

Quick META Keywords Plugin

5. Permalink Redirect
Permalink Redirect will issue a 301, permanently moved, redirection to anyone accessing your page via the non-permalink URL.

Permalink Redirect WordPress