The R820T is the tuner chip that is used in the most popular RTL-SDR dongles. It turns out that there is also an R820T2 tuner chip available, but it does not seem to be used in any RTL-SDR dongles that we know of. According to superkuh’s RTL-SDR notes, the R820T2 has better sensitivity over the R820T with an apparent 6dB lower noise floor. It also has a wider IF bandwidth which makes no difference to the RTL-SDRs 3.2 MHz maximum bandwidth, but is why the Airspy with its 10 MHz of bandwidth is using the R820T2 in its design.
Nobu an RTL-SDR experimenter who had previously experimented with dongles retrofitted with TCXO’s has now retrofitted a standard RTL-SDR dongle with an R820T2 tuner chip (note that this post is in Japanese). The Google translation of this post is a little to difficult understand, but it seems that Nobu did notice an improvement due to the lower noise floor. If anyone can understand Japanese we’d appreciate confirmation on this in the comments.