Thanks for the welcome!
Special relativity boggled my mind when I first learned it; it sparked my physics interest, so it will always remain one of my favorites. I'm taking a QM class and I find that material fascinating as well.
In general, I'm most enamored with physics in relation to thinking about the workings of the universe -- unintuitive concepts that are nevertheless true catch my eye like nothing else. I'm a reductionist at heart I guess.
And what are your favorite topics?