Patent Technology Monitoring Team reports. The link can be found in the "Products and Services"page.
Yearly reports are provided for seven categories, such as by technology, geographical region and patenting organization.
Statistics Index page
The last patent link for >Miscellaneous Patent Statistics, Other Web Pages< lists numerous sites within the USPTO and in a few other agencies.
If you do not find the information you are looking for in the general page, the "Other Web Pages" should be consulted.
USPTO "Dashboard" Page
From the "data visualization center", shows analog counters and graphs with stats from the current month.
If the graphics do not load, access the page via the "Index" page link above, >USPTO Data Visualization Center -- Patents Dashboard<.
Patent Trial and Appeal Board (PTAB) Statistics
Five statistics categories from the PTAB.
USPTO Re-examination Information Statistics
This is one of the additional web pages contained in the "Miscellaneous / Other Pages" listed above.
Operational statistics are provided, as well as historical stats on requests for re-examination from 1981 for ex parte requests, and from 1999 for inter partes requests.
Patstats.org
A web service from the University of Houston Law Center. Maintains statistics since 2000 for 40 patent case issues or types.
Also includes verdicts and occassional reports.
U.S. Ct. of Appeals for the Federal Circuit
Yearly reports for case category filings and more. In 2013 patents accounted for 46% of the caseload.
The University of Texas engineering library, includes a useful section on Patent Statistics as part of their patent searching tutorials.
The section includes explanations for constructing your own custom statistics reports.
Statistics through 2014 from the DNA Patent Database, a collaboration of Georgetown and Duke universities.