I tend to be a little more "multimedia" than just sticking to book recommendations, but I will weight my recommendations first to books and then mention the other resources:
You Can Do It!: The Merit Badge Handbook for Grown-Up Girls
“The text-patterned after a Girl Scout manual-is made up of seven "badge" categories (e.g., "Dare," "Create," and "Learn") that are further organized into activities such as learning to skydive and care for one's car and building family rituals or breaking bad habits. Each badge takes readers through the task from start to finish and includes excerpts from professionals in that field.” (LibraryJournal)
The Daring Female's Guide to Ecstatic Living: 30 Dares for a More Gutsy and Fulfilling Life
“Entrepreneur/author Kogan encourages readers to break old patterns and live outside the box through 30 "dares," or suggestions for living. The dares are organized into six chapters, which range from establishing better daily habits and eliminating unproductive fears to aiming higher and laughing a lot. Within these short chapters, Kogan proposes learning something new each day, e.g., dedicating six weeks to kicking a bad habit.” (LibraryJournal)
Fortytude: Making the next Decades the Best Years of your Life--through the 40s, 50s, and beyond (recommended for all ages)
“Through her experience in leading discussion groups with women nationwide, licensed therapist Brokaw knows that women who travel through midlife most easily are those who've fostered five core values-grace, connectedness, accomplishment, adventure, and spirituality-which empower them to be their most authentic and actualized selves.” (LibraryJournal)
Non-Book Resources
The Big Scout Project - a website/blog devoted to the one woman's efforts to expand her horizons by working through the Girl Scouts' "Junior" badge handbook.
The Julie/Julia Project (original blog) - Julie Powell's original and unassuming blog chronicling her efforts to move through her own quarter-life crisis is inspirational in its honesty and determination. I do NOT recommend her novel based on this blog - the original material is so much more genuine.
I'd love to hear your impressions or experience with these titles. Good luck!