What are the grave (major) sins?

Some of them are as follows:

1- To hold a bid’at. [Any change or reform made in the religion is termed a bid’at. It is a grave sin to hold a bid’at pertaining to tenets of belief and acts of worship.]
2- To continue committing sins.
3- Not to render your gratitude for being a Muslim.
4- Not to have the fear of dying without îmân.
5- To commit oppression.
6- To be rebellious to your parents.
7- To swear oaths very often, even if they are true.
8- Not to attach importance to learning the namâz [ritual prayer] and teaching it to your children.
9- To drink alcoholic beverages.
10- To make others think you are a pious person, though you are not.
11- To belittle your sin.
12- To have self-love.
13- To hold yourself superior to others on account of your knowledge and acts of worship.
14- To be jealous.
15- To say that a certain person is “good” before testing him/her.
16- To continue telling lies and backbiting.
17- To avoid the books of Ahl as-sunnat savants.
18- To maltreat your neighbors, even if they are disbelievers.
19- To get angry very often for worldly issues.
20- To practise sorcery.
21- To give up visiting your mahram relatives who obey Islam.
22- Not to love those whom Allahu ta’âlâ loves, and to love those whom He does not love.
23- To feel hatred of your Muslim brother for more than three days.
24- To commit fornication, adultery, or sodomy.
25- Not to cover yourself as Islam has commanded.
26- To commit murder.
27- To steal.
28- To take narcotic drugs.
29- To commit usurpation.
30- To eat publicly in the month of Ramadân.
31- To pay fâidh [interest] without a darûrat.
32- To devour the wealth of orphans unjustly.
33- To cheat in measuring or weighing.
34- To perform namâzes [ritual prayers] before or after their due times.
35- To break others’ heart.
36- To accept a bribe
37- Not to give the zakât and ‘ushr of one’s property. [zakât: (fard duty of giving annually) a certain amount of certain kinds of property given to certain kinds of people; ‘ushr: the zakât of production obtained from one’s land is termed ‘ushr.]
38- To burn a living animal.
39- To forget how to read the Qur’ân al-karîm after learning it.
40- To despair of Allah’s Mercy.
41- To commit perfidy.
42- Not to love any of the Ashâb-i kirâm.
43- To call chaste women unchaste.
44- To spread gossip (carry words) among Muslims.
45- To expose your awrat parts or to look at a person’s awrat parts.
46- To breach of trusts.
47- To be stingy.
48- Fondness for the world.
49- Not to fear the torment of Allahu ta’âlâ.
50- Not to accept a harâm [a thing that is prohibited] as harâm and a halâl [a thing that is permitted] as halâl.
51- To believe in what soothsayers say.
52- To look at women and girls, that is, to look at harâm.
53- For women, to wear like men and vice-versa.
54- To remind people of your doing them favors.
55- To swear an oath with any name other than Allah, for example, to say, “May I kiss my child’s dead body!”

56- To be a perpetual committer of a venial sin.
57- To remain junub [one who does not have a ghusl] so long as to miss a prayer time.
58- To play and listen to musical instruments.
59- To commit suicide.
60- Not to learn your religion.