~.~.
If you want to stick with Thomas sets, you have plenty of options. I have a ton of play sets for the Take N Play set. Those are the metal trains with magnets and the gray plastic track. Some of the trains will make noise and say sayings as you push them. Those have to be pushed manually. You can buy sets that snap together and extension track pieces. I swear, it seems like I have the entire island! One of the things I like about these sets are that they fold up. The trains range from about $6-9 each at Walmart, depending on if they talk or not. I bought about $300 worth of trains and track from a lady at work for $45. See if you could find someone selling. They hold up very well. This is what those sets look like.
http://www.amazon.com/Thomas-Friends-Take-n-Play-Rumbling...
Thomas also has the Trackmaster sets (brown track), where the trains move themselves with a battery. There are also sets with buildings that you can snap together and add extension track pieces. My son only has a couple of those and I don't really like them. They are too noisy to me, the tracks take up more space, and the trains are more expensive. Here's one of those:
http://www.amazon.com/Thomas-Train-TrackMaster-Rides-Star...
Thomas also has the wooden set, but I could never find those easily in the stores, so I stuck with Take N Play. Good luck!