Though the Arduino is a great device, I would like to see these improvements in the next generation of Arduinos:
Mini-USB port: Though the classic Type A USB is used for printers so people generally have them, they are bulky and generally do not have wall socks to power them unless a wall powered USB adapter is used. The Mini-USB is much more common being used with mobile phones and small devices. With this port we can use our mobile phone chargers to power our Arduinos and have a smaller less bulky port.
20 MHz Clock: Fast clock means faster calculations. Though it may use more power, it would be nice to still have an option to have then to be stuck with just a 16 MHz clock.
Crystal instead of Ceramic: Crystals are more expensive and require external capacitors, some of us like to have precision with our designs. >
Please post any recommendations you have as well