An excommunication is a particular type of Church penalty known as a censure. Censures are what are known as "medicinal penalties" (canon 1312 of the Code of Canon Law, section 1, note 1), meaning that their primary purpose is to help a person realize just how seriously wrong their actions have been, and encourage them to reconcile with the Church. For this reason, I'd be surprised if there were a formal list kept—it's not a "Ten Most Wanted" list. I'd expect the number to be pretty low, in the dozens or less (out of more than a billion Catholics) every year.

Per Canon 1331, excommunication prevents a person from receiving most sacraments, except in danger of death; from celebrating the Eucharist (if the offender is a priest); from exercising any ecclesiastical offices (for example, it might prevent a bishop from ordaining priests, or even from moving a priest from one parish to another); and from being granted any official positions within the Church.

The Church recognizes two types of excommunications: latae sententiae, which are incurred simply by doing an act, and ferendae sententiae, which are formally declared by an ordinary (usually a bishop), following an ecclesiastical trial. Most excommunications are intended to be ferendae sententiae, not affecting a person until the penalty is specifically declared. Canon law doesn't specifically state "the following actions are to be punished by a ferendae sententiae excommunication"; instead, it routinely uses the formula "X is to be punished with a just penalty", which is not necessarily an excommunication (reserved for the most serious cases).

Church leaders are specifically told to minimize the number of excommunications formally declared:

Penalties are to be established only insofar as they are truly necessary to provide more suitably for ecclesiastical discipline.

(Code of Canon Law Canon 1317)

A legislator is not to threaten latae sententiae penalties [which can include certain excommunications, as described above] except possibly for certain singularly malicious delicts which either can result in graver scandal or cannot be punished effectively by ferendae sententiae penalties; he is not, however, to establish censures, especially excommunication, except with the greatest moderation and only for graver delicts.

(Canon 1318)

A penal precept is not to be issued unless the matter has been considered thoroughly and those things established in canons 1317 and 1318 about particular laws have been observed.

(Canon 1319, section 2)

Furthermore, there are certain cases in which excommunication simply does not apply: in which a person cannot be excommunicated. First of all, the offender has to have done the act in question deliberately, and "with malice aforethought" as it were. Without this, there can be no excommunication:

No one is punished unless the external violation of a law or precept, committed by the person, is gravely imputable by reason of malice or negligence.

(Canon 1321 section 1)

A whole bunch of groups of people are excluded from being excommunicable:

1. a person who has not yet completed the sixteenth year of age;
2. a person who without negligence was ignorant that he or she violated a law or precept; inadvertence and error are equivalent to ignorance;
3. a person who acted due to physical force or a chance occurrence which the person could not foresee or, if foreseen, avoid;
4. a person who acted coerced by grave fear, even if only relatively grave, or due to necessity or grave inconvenience unless the act is intrinsically evil or tends to the harm of souls;
5. a person who acted with due moderation against an unjust aggressor for the sake of legitimate self defense or defense of another;
6. a person who lacked the use of reason;
7. a person who without negligence thought that one of the circumstances mentioned in [points] 4 or 5 was present.

(Canon 1323)

So if you're a minor, or if you were (or felt) coerced into an action, or didn't know that what you were doing was forbidden by canon law (and I emphasize this because very often Catholic lay people aren't aware even of the existence of canon law), or if you were reacting to a situation over which you had no control, or if you thought you were behaving reasonably in self-defense, you cannot be excommunicated. Period.

The three specific instances you bring up—extramarital sex, premarital sex, and the use of contraception—are certainly grave sins: but they are not excommunicable offenses. Excommunicable offenses might be things like a priest (who is not a bishop) trying to ordain a priest, or a person physically assaulting their bishop or the Pope. The things you bring up are sinful, but they don't indicate (as these others do) a malice toward the structure and nature of the Church itself.