One of each of our favorite Mifare Classic 1K tags - 5 in total!
These can be read by almost any 13.56MHz RFID/NFC reader but make sure it can handle MiFare cards as there are a few other encoding standards (like FeLica) They are tested and work great with both our PN532 NFC/RFID breakout board and Adafruit NFC/RFID Shield for Arduino!
These chips can be written to & store up to 1 KB of data in writable EEPROM divided into banks, and can handle over 100,000 re-writes. You can use our PN532 NFC/RFID breakout board or Adafruit NFC/RFID Shield for Arduino to read and write data to the EEPROM inside the tag. There is also a permanent 4-byte ID burned into the chip that you can use to identify one tag from another - the ID number cannot be changed.