Check with your local shop, most likely they have informal ride club rides that meet on the weekends at the shop or a local coffee shop. They may offer various level of rides, so be honest and let them know your abilities and comfort.

Also, consider riding some organized rides, usually a charity find raiser. The masses and riding with others is great motivation and you'll always find someone of your like abilities to chat with. A good example is the Ojai Valley Century in Ventura County next weekend. I believe they offer four or five different routes: 34-, 62-, 100, 134-milers. Organized rides usually have rest stops every 20 miles and you're always in good company.

I enjoy solo, but I also enjoy riding with others - probably a 50-50 mix for me.