er...I don't know what you mean by "without reading any books"... but if you mean playing by memory, I can play just about every opening, my usuals being the Ruy lopez, the Italian game(my first opening), the Sicilian, the French, the Caro-Kann, Etc.
your natural opening
After being taught only the rules, I opened my games playing 1. d4 2. Nc3 3. Bf4. I stopped using it after I was introduced to "real" openings like QG and the ruy, but have recently started using the richter-veresov (3. Bg5) and have really enjoyed it.

D4,B4,C3.
An ugly move set but it can claim some turf on the queen side, and its not bad as long as you watch the hole in your pawns carefully.

I love the Danish so much. People keep telling me not to play it in slow tournaments because its technicley not entierly "sound" but its so much fun.

I play e4 followed by f4 as white nearly all the time, against most black replies.
As black i play modern defence g6 and fianchetto.
i€ feel most comfortable with these systems

I started playing the birds opening (f4) unknowing of the Title "Bird" it would have to be my favorite white opening ... Since learning the name Ive practice it and use it almost every chance I can
http://www.chess.com/forum/view/chess-openings/bird-bird-bird--bird-is-the-word

I play just about anything, King's Gambit and the Nimzo-Indian being my favourites, (opposite styles, but equally effective)

I don't even really play it that much anymore, but honestly, it's probably the Sicilian Scheveningen.

My natural opening is the Reti-once you know thew basic set up, move order doesn't matter. The only variation Black plays that you need to watch is the d pawn push.

Now my most comfortable opening at this point is hands down the Benoni ... It gives me targets which is my strong point.
However if I was to play chess with no knowledge of openings, I'd probably be playing the exchange variation of the ruy lopez or the scotch 4 knights.

Without having studied any openings in depth my inclinations, for either colour, are to get the kingside knight out in front of the pawn, and the queenside night out behind the pawn.
Then push forward the center pawns and move the bishops and queen off the back rank to connect the rooks. I focus first on the kingside bishop to facilitate castling.
pawn storms are always fun ;)