We just had a great train party with 20 toddlers.  We rented a party room in New York City and hired Lou Gallo (imagination workshop band) to play guitar and sing original (e.g., "subway train") and classic children songs.  I made the birthday invitation "Birthday Express"& thank you notes on my computer using clipart & MS publisher. Decoration: Using MS Publisher and clipart made 25+ poster sized print outs of trains, traffic signs, and phrases, printed/pasted custom poster sized pictures onto large cardboard boxes & cut out holes for the windows, smoke, etc. to climb/peek through, balloons, Thomas table covers, blue/red dinnerware.  Activities: Train boxes, pop-up vehicles/tents/tunnels, balls, crayons, bubbles, and train coloring pages (clipart minus color).  We made a pin-the-train on the tracks game but never got to it. Food:  Crudits (carrots, cucumber, grape tomatoes), hummus dips, salad, pizza, and cake with a train picture on top & train candle.  Favors: Individualized laminated train placemats using 8 1/2 x 14 paper, plastic train whistle, and a train shaped sugar cookie (baked & froze until the day before and then decorated using colored frosting, nonpareils, and an icing from confectioner sugar, vanilla and milk).  Thank you to all the other moms who posted ideas and helped me to generate my own ideas. Hope you have a fun party, too!