There are dedicated threads for the various DVRs that don't require subscriptions, which include:
The DTV Pal / CM-7000 Pal are also options, but they have been out of production for a while and may be more difficult to find.
Be aware that Comcast is planning to stop offering unencrypted cable nationwide in the next year or so. When that happens, you'll probably be forced to upgrade to the more expensive service plan, and all of these DVRs will be come useless with Comcast. If you can use an antenna in your area, you could still use these DVRs for OTA TV and cancel your cable service completely.