Pyraminx you should definitely figure out by yourself. It's the easiest of the WCA puzzles by far.
Megaminx takes a bit of thought to translate stuff you already know to feel with 5 sides instead of 4, but its a good test of whether you actually know how to solve a 3x3.
Skewb is tricky but not too difficult to figure out once you understand how it turns. It takes a lot more patience and experimenting with various sequences of moves to see what happens to find something useful. I've seen even non-cubers manage to solve the corners within about 5 minutes of first picking up a skewb. Centres are the tricky part.
Square-1 is fairly easy to work out barring two things. Firstly, it can be hard to work out relationships between the shapes at first. Secondly, I don't think I'd ever have had the patience to work out parity on my own.