Wired reports on the Navy's Higher Speed Antiradiation Demonstrator (HSAD) project, an upgrade to the AGM-88 HARM missile. The NSAD rocket uses its combustion chamber as a ramjet, making it a 'ram-rocket'. They expect "twice the range of the current HARM at two to three times the average velocity as HARM." Velocity estimates are M3+ to M4+.
This is not a new concept and has even been researched for sport rockets. If the old TRF archives were up I could provide a thread that links to the related documents. I thought I had already done so, but didn't quickly find the post, and didn't look hard since it would only point to the (hopefully temporarily) missing post. These articles, by Chuck Rogers, came from July 1982 and October 1982 issues of California Rocketry magazine. IIRC they were hosted by US Rockets, but I couldn't find where. Luckily, I grabbed them :) There is a also a related post on Rocketry Planet. I am really batting 000 on this issue. If you have additional links, please leave them in the comments.