Open source development projects often welcome testers. Mozilla is an obvious example, with its QMO site. There is also uTest, a commercial site that hosts "crowdtests." Registered testers get paid for the approved bugs they find on customer-submitted applications. Particularly for new testers, this can be a useful way to gain hands-on experience. For experienced testers, sites like these provide opportunities to try out techniques away from their work.
Joining your local quality group is a great way to share experiences (and job opportunities) with a wider group of testers than you usually work with. Such groups often have interesting speakers, and they also provide opportunities for their members to present. Search on ASQ, SPIN, QAI, and APLN (and in Canada, CIPS) for local chapters.
Start Your Own Group
If your community doesn't have a quality group, why not start one? You'll gain opportunities to learn from the speakers you engage and get valuable management experience. Do you need practice in negotiating, or perhaps in saying "no"? Create a group with others who are similarly interested, to share tips, role play scenarios, and critique each other. You could base sessions on problems your members face or on lessons from books. Or start a lunch-hour book club with tester colleagues, reading and discussing the ideas in professional books and trying them out in your work. A test manager I know hosts weekly "thinking" sessions with her team, where they play games and do puzzles and exercises designed to enhance their thinking skills while having fun together.
Most communities have innumerable opportunities for volunteer work where you can learn new skills, as well as gaining the satisfaction of making a contribution. Both hands-on and management work have benefits for volunteers.
Charities such as women's shelters, legal clinics, hospices, humane societies, housing cooperatives, amateur cultural organizations, sports clubs, and all sorts of other community organizations are usually run by volunteer boards. Many would love to give you opportunities to develop and explain a budget, work on a marketing campaign, hire staff, negotiate agreements, or do a myriad of other tasks that will enhance your business skills and teach you new ones. Some organizations have seasoned professionals happy to teach you; at others, you might have to figure it out by yourself.
Hands-on work has special rewards, whether you're answering a suicide help line, joining others to build community housing, or helping seniors fill out forms. An activity that helps you grow as a human being will also make you a better tester.