I think Kate_Canuck's idea is great (re: taking classes). While I tend to not like tours, I have considered doing an activities based one (e.g., biking through Loire valley or a cooking based one) & I bet you would meet more like minded people through that.

My other comment would be -- I don't like traveling alone, either. Although I'm capable of doing it, it just makes me that much more nervous to have to watch my stuff all the time, etc. It's tough to predict in advance who you're going to like traveling with, and I agree that sometimes it's awful, but I've actually had surprisingly good experiences expanding my potential travel buddies circle beyond my closer friends. It can sometimes work better that way, actually, because if you're not that close to begin with, there isn't too much friendship to strain. I recently signed up for dopplr.com and it's a good way of keeping track of where people are going and where your schedules might coincide.

Also, it may not be something you're comfortable with, but in the "budget travel" forum, there was recently a thread on couchsurfing. FT-ers report positive experiences with it. It might be at least a way for you to meet people at your destination, once you've chosen one.