Parallax sells a Smart Card reader for $10. They also have cards for $1.25 (it looks like these cards just have an EEPROM, not a microcontroller).
Edit: I think the Parallax reader can just read the card. I don't think you can program Smart Cards with it. I think this is why is costs so much less than the other devices mentioned in this thread.
When I initially wrote this post, I thought Smart Cards were similar to RFID cards but which needed contact to read. As the OP suggested, Smart Cards have embedded microcontrollers which allows them to do many things a RFID card can't. Here's a link to the Wikipedia article on the topic. The rest of my original post is pretty much worthless.
I don't think the chip inside the Smart Card is a full fledged microcontroller. I think it's just an EEPROM. I think a Smart Card can just be used for storing a bit of data (okay it can store more than "a bit", it can store many bytes).
MIFARE RFID readers are less expensive and I think the cards cost less as well. The RFID cards have password protected sectors.
I've never really seen an appeal to using Smart Cards since the RFID cards seem to do the job just as well and cost less.
Of course an RFID card can be read without your knowledge but I don't think hacking the data on the card is a trivial matter.
Edit: I've been reading some of the links about Smart Cards and I learned I don't know much about Smart Cards. Interesting stuff.