CyanogenMod10 has been the first taste of Jelly Bean for many devices. Until now we have mostly been running on unofficial builds and ports. Yesterday the CyanogenMod team announced that they would begin M-Series releases to come out on a monthly basis. M probably standing for Milestone will be a stable build with most bugs from regular nightlies squashed. They will be releasing the M-series builds at the beginning of each month. Apparently the CM team had a soft-code freeze where they stopped adding features and focused on cleaning and bugs to make the first Milestone build as stable as possible. The new M-series builds are still labeled as experimental so they will not be 100% perfect. This will initially be released on 18 devices including the Galaxy Nexus, Galaxy S III, and Nexus 7.
You can download the builds from the CM download page.