I love croutons... I'm not a fan of salad, but I snack on croutons... but have you ever looked at the ingredient list on some brands? Not to mention, it's actually pretty easy to turn ingredients you already have into yummy crunchy goodness without leaving home.
I'll share with you my method, it's not an exact recipe, because it will vary based on your personal preferences and the quantities you have on hand.
Start with your bread. You can use fresh bread or stale bread, doesn't really make a difference in the end. The only difference is that the fresher the bread, the longer it will stay in the oven, in order to dry it out. Most recently I made some croutons with some leftover Sourdough bread I had. It was a really rustic bread and had lots of flavor, but you can really use any bread you want.
Cube your bread, size is up to personal preferences. I usually cube mine in about 1 inch or so pieces, because I like jumbo croutons. If you make them smaller, they'll finish faster of course. You'll want them to be similiar in size, so they'll all finish at the same time.
Spread the bread out on a baking pan and drizzle with melted butter (for a full pan, I use about a 1/3 a cup of butter) you can use more or less, just eyeball it, the more butter you use, the better the end result. Sprinkle the bread with your favorite seasoning (I use garlic powder) and then toss the bread cubes to make sure they are coated as evenly as possible (you don't have to be perfect)
Bake the bread @ 300 degrees until lightly browned and completely dry. You'll want to stir them every 10 to 15 minutes. I usually bake mine for about an hour and 15 minutes. These are a good project for when you're cleaning the kitchen, etc, since you'll already be in there. After about 30 minutes, I usually take them out and drizzle/stir in some additional melted butter (maybe another 1/4 cup) and some more garlic powder.
When you think they are done, taste one... if it's chewy in the middle at all, go another 10 minutes and try again. At about the 1 hour mark, I take mine out and sprinkle in some grated Parmesean cheese (toss to coat) and let them go another 10 to 15 minutes. Once they're done, to ensure that they are completely dried out and nice and crunchy, I just turn the oven off and leave them in the oven to hang out for awhile.
You can store them in an airtight container, or in the freezer for longterm storage.