I am a huge fan of Melissa and Doug toys for both speech therapy and my own son. Some of their items can be a bit pricey, but their Reusable Sticker Pads are very fairly priced at about five dollars and GREAT for speech therapy!
I got the habitat sticker pad as a gift from a fellow SLP last year and use it all the time. I just ordered the vehicles pad. Now I have my eye on the play house pad! Oh the possibilities!
Here is how I've used this in therapy:
Categorizing: Have the kids sort and group the animals into their correct habitats.
Vocabulary: Work on naming and labeling the animals to introduce new vocabulary.
Following Directions/Prepositions: Give one to two step directions, while also addressing prepositions by telling the child which animal the place on the pad, as well as where (place the whale above the lobster, etc).
Describing/Comprehension: Have the child describe the animals using adjectives/descriptors. You could also have them listen to your descriptions to work on comprehension/listening skills (point to the long, red animal with pinchers)
If you are looking for some cheap and versatile speech materials, check them out here!