Here is a website that has a list of fish that have high levels of protein:
Protein in Fish how much protein in different fish good protein source
Here is a website geared towards vegans that has a nice list of protein values for different foods:
Protein in the Vegan Diet -- The Vegetarian Resource Group
Spinach, Broccoli, Tofu and Eggs are good sources of protein. Almonds as a snack are not a bad idea.
If cheese, check this out:
Protein in Cheese
Meats are high in protein, but they are also oft-times high in fat. Depending on the type of meat.
Also something to keep in mind: The preparation of foods may increase or decrease the digestibility of the protein. You may want to do a web search on that.
Protein is relatively easy to get through normal eating (in fact, most people in first-world countries actually consume more protein than is recommended), only slight adjustments are required to boost the level of Protein you're getting. I'd also suggest stopping by the library and look in the section between 610-620 (Dewey Decimal System, others will vary), somewhere in the middle there are books about health/diets/working out (recipe books are 636, those might help too). Browse those to see what you can learn about getting the necessary amount of protein to help you build muscle mass.