I, as well as numerous others on here, know all the pokemon theme songs by heart :D minus the ones after Master Quest because they don't exist to me. I know that means I don't know them all by heart, but I stopped watching after Master Quest soooo...
My favorite theme songs are from sitcoms in the mid 80's early 90's because I grew up watching the re-runs as a kid :) and I used to memorize all the songs (well, as best as I could because looking back now I realize I butchered a lot of the lyrics). I would always sing to the theme songs of Step By Step, Full House, Family Matters, Boy Meets World, and then even though there were no lyrics, I also enjoyed The Cosby Show themes too since they changed them a lot, especially the elevator music one.
However, out of those I mentioned above, my favorite theme song of all time is the Growing Pains theme song :) I sang that one the most and I just plain enjoyed the song. "Show me that smile again, show me that smile. Don't waste another minute on your crying, we're nowhere near the end, the best is ready to beeeeegin" <3