Anything closed.
Lets Put Together A Boring Repertoire

No boring repertoire would be complete without the London System (1.d4 2.Nf3 3.Bf4). We actually used to call that opening, "The Boring".

Can't believe some of these lines are being called boring! Positional chess holds more interesting facets than tactical in many cases!
If you want boring you're looking at lines that are likely to draw regardless of who manages to build the better 'minor advantages'. The Petroff has that to some degree.
As it stands now I think the only line I could possibly call boring is the Berlin Defense in the Ruy Lopez.

i agree with ih8sens because iv played against the stonewall and and the colle and they did not turn out to be boring games. I think the stonewall is a good secret weapon aswell.

ih8sens, I must be a goofy goober. I also think many of these boring lines can lead to exciting games--it's up to both players. Someone said "QGD". What?! Some lines of the Slav are as sharp and complex as any position is chess. And even the QGD / Exchange creates imbalances and interesting strategic struggles.
Anand was taken down in under ten moves in the Petroff... and then there's the Cochrane Gambit; perhaps unsound, but surely interesting... and that game where Petroff plays White and takes down a team of amateurs playing the Petroff!
Of course, the open file and symmetric pawns leads to many quick draws.
The most boring is Giuoco Pianissimo. Don't underestimate Petroff. You should be careful playing it with Black, I lost a few games in a row after all the book moves. The play is open and there no Nf6 to defend your king. You easily can get under attack on the kingside or in the center.

I completely disagree about the petrov, in many of the sharper lines where White isn't content to just settle for equality Black has many attacking chances.. In fact I can't really think of any prominant openings that I would consider particularly 'boring' but that's just me. I've been playing to death probably one of the most commonly considered 'boring' openings of them all lately the 'Torre Attack' and am thoroughly enjoying playing the typical 'slow squeeze' middlegame positions.

I continue the movement that promotes Petrov's Defense. It's my main play against 1.e4, usually, and if you play it right, you can launch many attacks.
Another thing, everyone bashes the Italian game, but have you ever tried Evan's Gambit? Italian Gambit? Italian Gambit: Miami Variation? These openings are naturally positional but can be tweaked to become "fireworks lines."
The Colle System is not boring either. I don't really know if some of you just played with these/ against these openings just once and then passed a judgment, but I don't think many openings are actually boring.
In the end, the player's style is what makes a game "boring," not the opening, although I do agree that some openings are naturally more passive than others.
(Sorry if that sounded harsh)

The most boring is Giuoco Pianissimo. Don't underestimate Petroff. You should be careful playing it with Black, I lost a few games in a row after all the book moves. The play is open and there no Nf6 to defend your king. You easily can get under attack on the kingside or in the center.
The Closed Giuoco may be more boring than many other openings but as a player that adopted it years ago, I can tell you black tends to be more put off by the turn of events than in other openings. Why? Probably lack of acquaintance and the likelihood of going into a completely different kind of game than they envisioned after meeting e4 with e5.
So boring? Ok, but with not a great deal of study I get pretty good positions typically.

I pretty regularly opt for the Two Knights Defense which either equalizes (according to Fischer and after d3/Nc3, Nxe4!) or leads to fireworks after Ng5.
Just been looking at the Petroff. This must be a candidate for the most boring opening out there - but it does seem principled, "standing toe to toe" ..
I like interesting opening as much as anyone else BUT against a particular opponent on a particular day, at a particular time in a tournament, say, perhaps it might be good ploy to try and bore the opponent ? and just perhaps, to be able to adjust one's boredom threshold to level where the Petroff etc are interesting represents a worthwhile challenge ?
I would suggest :
1/ The Petroff against 1e4 e5 2 Nf3
2/ Queens Gambit Orthodox
3/ As white, the Reti or Stonewall
:)