This site acts as a front-end to both 3GPP and IETF major SDOs, by offering consolidated information about their standardization work.
There is a full coverage of the technical specifications and reports produced by the 3GPP working groups with a quarterly update, following the TSG Plenary meetings. The drafts also are included, and their status gradually updated.
The IETF defines fundamental protocols used by the 3GPP as well as nearly all other SDOs. In regards to the 3GPP EPS, we can mention