If you want to take the easiest quickest approach paypal is one way to go.
You generate the paypal button on the paypal website. Then you place it on your website. You can then have someone manually confirmed payments went in. If you want to take it a tad further you can setup IPN (instant payment notification) where paypal will connect to your server, authenticates itself and tell you that someone just paid succesfully (or not). Its all pretty easy and there is some source code out there.