Lego Duplo + Thomas the Train lots
We just received a huge lot of several Lego Duplo sets, a bunch of Thomas trains and gear, AND a Thomas Duplo Starter Kit Set ( #5544 ). If you're into Duplos (which is to say: if you're in to one of the best preschool toys around) you should get here soon; these don't come easily second-hand.
Duplos, imho, are even better than Legos proper because kids can actually play with them. If you lose a piece or two, the set isn't automatically obsolete. Like old-school Legos, they allow for open-ended play and the pieces easily interchangeable.
The Thomas set is $50, complete in box (currently selling for $400 on the collectors market - it originally sold for $80).
We also have have Duplo construction, fire truck, Toy Story, and a few other sets for $20 or less. And, as mentioned earlier, we have several non-Duplo Thomas sets, including many wood trains and tracks, and a few Take n Play sets.