Like Glory, I have a spreadsheet I created to do this. Most of my recipes are glued to index cards, so I print out the spreadsheet and glue it to the back of the card. But there are free online tools that can do this analysis for you--try
www.fitwatch.com (the free version not the deluxe) or
www.nutritiondata.com.
As to figuring out servings when they aren't specified, sometimes I work backwards based on how many calories I want each serving to be. Tuna salad is a great example of this. Let's say the entire batch of tuna salad has 900 calories and I want each individual serving to have around 300 calories. I would divide it into three servings. If I want each serving to have only around 200 calories, I would divide it into 4 servings.
If I have a recipe that says how many servings it makes, I usually go with that. There are a couple of exceptions to this, however. If the servings seem too small to me or the calories in each serving are really low (usually a sign that the serving size is too small), I'll redivide the aggregate calories by the number of servings I actually think it will be. If the calories per serving are a little high, sometimes I'll add more veggies and then increase the number of servings to get to a calories per serving I'm happy with.