The Nooelec store have recently come out with a new small RTL-SDR model called the Nano 2, which appears to an improved version of the old tiny square dongles. These new ones are sized at 24mm x 21mm x 8mm and come in a new plastic case with vent holes to prevent overheating. They also come with the newer R820T2 tuner chip. This appears to be a good improvement over the older models which were reported to have overheating and thermal frequency drift issues.
These small dongles look to be great for embedded or mobile phone applications that have space restrictions.
The new dongle is currently selling for $24.95 USD + $1.99 shipping.