Hi, Amber!
Always be cautious when ordering tickets outside of Disney. I am NOT saying they are not legitimate, I really have never heard of them. However, tickets are only valid if never used as tickets are non-transferrable between guests. There is also no way to check the validity of the tickets until you are actually in Walt Disney World, and if there is a problem, you are stuck.
That said, I have purchased tickets that have a slight discount through my local AAA office and also through a website called undercovertourist.com. I would recommend both places.
Remember, if you plan to purchase a vacation package while visiting Walt Disney World (including the Disney Dining Plan) you will need to include park tickets, so plan before you buy all your tickets. If you are planning to book a "room only" reservation or are staying off property, then buying your tickets ahead of time is a good idea.
There is always the guaranteed success of buying right through Disney. You can purchase tickets online at
www.disneyworld.com or at the gate, whatever you are most comfortable with. I hope this helps!