I am looking for an addon aircraft (737-700). Any ideas on a website that I can download one? What are the advantages and disadvantages of them? Thank you all for your help!

There are some good reworked Posky packages at the Avsim library. One of the Southwest packs comes to mind. They are not too bad, add a panel of your choice or stick with the default. I've got mine merged with the Friendly panels 737ng pack.I have heard that the PMDG 737-600-700 will work in FSX on a limited basis in FSX, but thats not an ideal solution. The other that I know of is the Overland for FSX, its a very basic model not very far ahead of the default craft. The Wilco 737-500, 600 is a decent effort. Other than that I would suggest waiting for the PMDG 737NG when it comes out.