There are a couple of premium plugins for Wordpress that cloak your outgoing aff. links.
Here's a simple free method for one affiliate link:
1.) Make a folder. Name it "recommends", "review", "go", or whatever you want.
2.) Create a text file inside the folder. Give it the name of the product you're promoting
3.) Open text file and enter:
<?php
header('Location:
youraffiliatelink');
?>
Save.
4.) Change the extension of your text file to php. (textfile.php)
5.) Upload the folder to the root of your domain.
(NOT the root of your server)
6.) Test it. Easiest way to test it is by using a Clickbank aff.link. Click through to the order page and check if your affiliate name is at the bottom of the page.
7.) Inside your content: when you make a link, you link to the file you created.
I.e.
Code:
http://yourdomain.com/recommends/product.php
(hope I didn't make a typo in the code. Been a long time since I did it this way...

)
Use this in the searchbox here on BHW to get some more ideas:
affiliate link cloak