Adding Custom Tabs On Facebook
As far as i know the most popular app used to make facebook custom tabs is Static FBML which no longer works now, there are many other apps out there that can help you achieve this but has its own problems like slow image loading and usualy a credit going back to them.
You can however use a facebook inbuilt developer app to make this.Follow these steps:
go to https://www.facebook.com/developers/createapp.php
put in the name of your app and agree
go through the security check unless you are a robot
under the About tab fill the proper application name and desired icon
go to the Facebook Integration tab (this where it gets tricky)
Give it a proper url name under Canvas page say something like (my products)
Canvas URL is the location of the file on your website where you want to pull the iframe from (eg. www.myhost.com/fbapp/)
if you have ssl then specify the same for Secure Canvas URL but use "https" otherwise leave it blank
choose auto resize if you intend to have your app wider then 520px then you will have too use Fb api to control that else just make sure your divs/imgs dont go beyond that
Under the Page tabs section- Give the tab name (like Products)
Tab url would be the same as canvas url and secure tab the same with https(if you have ssl on your server)
click on save changes
Go back to https://www.facebook.com/developers/apps.php and choose the app you just created, click on Application Profile Page, this will take you to the app and on the app page click "add to my page" and choose the page you want to add this to. and thats it your are done.
Problems?
The most common mistake you can make is not having your canvas and tab url set properly,make sure it points to a correct path, open the same url on a browser tab just to be sure.
If your file is a .html and returns a http 405 error then see what server you are hosted on and if the server uses php or asp or cfm and change the files extension to that and that should solve it.
If you dont have a ssl on your server then the users accessing your app thru a secured connection will be prompted with a message to leave thier secured connection and browse to your app with a normal connection.(sucks right!)
The beauty of this is that you can customize whatever you want in that iframe of course you have to be mindful of facebook's rules.