With the snow melted and the crocuses blooming, I like to walk my yard and play a simple memory game, as in "I wonder what I planted there?  And there?".  I can usually remember after a bit, once I've examined the spent leaves and any dead blooms I forgot to trim.  Although I have been known to accidentally pull out a desirable seedling mistaking it for a weed.  If you have the time and inclination, you can certainly buy fancy plant markers and have your yard resemble a pretty little botanical garden.  But working around those markers can be cumbersome and if you use the kind that you write on with a marker, the writing will fade over a winter and be illegible.  If you absolutely need to know what is planted where in the spring, it may be more beneficial to make a sketch of your yard and map out where you put your plants.  I, personally, am pleased by what survived the winter and don't want to be reminded if something didn't make it.