I recently changed my mortgage company, and I would recommend hunting around to find cheap mortgages. I compared mortgages and saved money and if you are looking to change mortgages or are getting a new one a comparison site is a great place to start.
I also believe that credit card comparison should also be done before you choose to get your credit card. I did this before I got my recent ones. I had to decide what I was going to use it for and then use this as a criteria for deciding which would be best for me.
I have also just made a massive saving on my car insurance by using a compare car insurance website. In fact comparison websites are great for any finance you want, even if you want to compare loans. Only you know what is best for you whether it be low interest, quick repayment terms or what and you should always make sure that you can get the best deal possible.