This is very important. Nothing comes close in importance when trying to gain lean mass than diet. I'd even rank it ahead of training (but obviously you need both). Supplements are very overrated. Not surprisingly seeing that the business is a multi-billion dollar industry (including fat loss pills) and fueld by "nutrition" and bodybuilding magazines who are owned by the supplement companies.

You say you only eat healthy foods and that's great. But you want to maximize your results so you'll need to be as specific as possible. Using FitDay is a great idea. When you know exactly how many calories you are eating and your macro ratios (what percentage come from carbs/protein/fat) you are in a great position. Measure your results every week. When you're stop getting results for a few weeks - change something! Usually in your diet. It takes a calorie surplus to gain muscle. It doesn't matter how hard you work in the gym if you don't eat enough calories. Weight training gives the reason for the muscles to grow, but food is what gives it the means to do it.

Once you master the calories you need to master the quality of the calories. It sounds like you are already doing this. The simplest rule is the closer the food is to how it came in nature or from the animal the better. Avoid processed food and the like.

After nutrition is under control and you're eating slightly above maintance the next area you can tweak is your training. Simply, make sure you do something more every session than you did the week before. As you know, if you continue to do the same thing week in and week out you will never move forward. Also, avoid overtraining, but avoid undertraining as well. Train hard every session, but always keep it under an hour.

Finally, supplements can come last. At least 95% of your results are going to come from the food you eat and how smart/hard you train. It doesn't make since to concentrate on the last 5% when you're not maximizing the first 95%. But when you get to this point you can push yourself to a full 100% of your capability with supplements. The most important being whey protein. Whey (in water) is great PWO because of how quickly it reaches the muscle. PWO you are looking for fast protein. I'd also suggest taking BCAAs directly before and directly after working out. Finally, you can add creatine. Creatine seems to affect some people more than others.

Best of luck.