I'm a fan of Smash books - I have three I purchased recently, but I actually started one of my own using the same concept, but with a regular journal instead of one with the offical "Smash" name.
I found this journal at TJ Maxx, but you can find them just about anywhere! The concept is simple. Just "smash" the item in the book using staples, glue stick, etc. I like it because I don't feel I have to go to my craft room and scrapbook an entire page for every tiny, little, beautiful item my kids make for me. I also like it because it is completely informal, but I can added embellishments if I'd like or not ,and I've saved a valuable piece of paper.
I might add that I do get giddy whenever they make something for me. I don't want to sound like it's a nuisance that I have to find a place to put it, because that's not the case. However, it's a common thing among households with children so I wanted to share.
I keep my little treasure journal, as I call it, on the kitchen counter in a basket. That way it is completely accessible at pretty much any given time.
Since I use it so often, my kids have started their own "smash" books and they feel proud when they see me put their little handy work in mine.
Like I said, it's not formal, but it still holds my treasures in one location for safekeeping and I like that!