BSA’s Cub Scout Program Helps is a great resource for Pack leaders and Tiger, Wolf, or Bear den leaders. The 2007-08 booklet is only $2.99 from your local scout shop or from scoutstuff.org. It contains a month-by-month breakdown of suggestions for den/pack games, songs, advancement ceremonies, crafts, and other activities to go along with the Cub Scout Monthly Themes.
BSA also includes the Program Helps pages for upcoming months as inserts in Scouting magazine.
And you can also get Program Helps information online. BSA includes the pages for the current month (January) and upcoming month (February) on their website at this link. (And it appears that they are now including links for previous months as well.) Link
The links in this post are now out-of-date, but the Cub Scout Program Helps link under the Blogroll box to the right has been updated.