Though I agree with the npg up there that touring bikes themselves are pretty versatile, I myself found myself at the point you are at and chose the cyclocross path. I had a lingering interest in actually racing cyclocross at some point so that made up my mind (for the record, I did follow that interest and have raced the last 4 'cross season ... love it!). There are several good steel cyclocross bikes that make for pretty comfortable touring rigs. I have the Soma Double Cross (
http://www.somafab.com/frames.html), which I love, but Surly also makes a Cross Check (
http://www.surlybikes.com/crosscheck.html) that gets good reviews. I am sure there are others. A steel cross bike is not ideal for racing, but I have a lot of fun on mine and I don't fare to poorly in my Cat 3 races. If you are not racing on your 'cross bike they still are good all around bikes and will serve you well in almost any capacity. Quick note about fit: I ended up giving myself more stand over than I would normally mostly because I was thinking about racing. If I had it to do again I would probably go one size bigger. The trouble with fitting your bike in this situation is that for cyclcross racing the traditional recomendation is a healthy 1 to 2 inches of standover. Touring is just the opposite, usually you are supposed to get the biggest bike you can standover at all. So, be mindful of that and think about what you are going to be doing with the bike and you should be all set.
Regarding panniers vs. trailers that is a personal taste question. For my part, I use panniers in back and a large handlebar bag up front. I pack light and the bike handles it like a champ. In this formation I have toured self-contained for up to a month.
Good luck and enjoy!