American Sign Language can be fun to learn. Nowadays the trend tends to be to teach our babies some simple signs to communicate at an early age. I like some aspects of it because, for instance with spelling, it gives a more tactile approach to learning. Plus, its great when one becomes fluent enough that she can actually interpret for deaf people.
The Start American Sign Language site has information on deaf history, deaf culture, an ASL dictionary, and more. You can also find free ASL lessons on the site. Simply follow the links. Its best to look closely at the course description first as it does suggest some optional materials that may make your learning more complete - depending on how seriously you want to learn. They also offer some lessons that are paid for at what seems a reasonable price. Its worth a look-see.
Just a personal story: I had a friend who was homeschooling her 3 teens. The colleges the kids were looking at required two years of foreign language in order to be accepted. But, the kids all had trouble learning foreign languages - try as they would, they just couldn't get a decent grade in those classes. The mom came to find out that ASL was listed as an option for foreign language credit. The kids took classes at the local community college and did great! They got their 2 years worth of credit. It wasn't without hard work, mind you. ASL isn't a walk in the park. But, for those kids, it was an option that worked better for them than learning a spoken foreign language.