My favorite command is 'say'. You can do all kinds of silly voices.
Try this out: say hello -v Good
Try this out: say hello -v Good
say -v cellos "Dum dum dum dum dum dum dum he he he ho ho ho fa lah lah lah lah lah lah fa lah full hoo hoo hoo"
python -c "print 'foo ' * 26" | say -v cellos wc -l < /usr/share/dict/words | xargs -I {} jot -r {} 100000 | paste -d " " - /usr/share/dict/words | sort | awk '{print $2 "! "}' | say gshuf /usr/share/dict/words | head -n 10 | awk '{print $1 "! "}' | saysay -v '?' (This gives you a list of voices)
say -v Good (This let's you type in a stream of text)
say --interactive=/green spending each day the color of the leaves