Assalaamu alaykum. Could you please claryify this sentence for us in this hadith: http://sunnah.com/bukhari/56/5...
"Who is next?" He replied, "A believer who stays in one of the mountain paths worshipping Allaah and leaving the people secure from his mischief."
What does that refer to? Is jihad not the greatest of acts that leads us to Paradise? What is jihad good for if the greatest act is to stay on some mountain path? Is there any other 100% guarantee to enter Paradise except through jihad in the Path of Allaah?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

It seems that the dear questioner did not understand the hadeeth correctly. It does not mean that the believer who is in one of the mountain paths is better than the mujaahid with his life and wealth, and not even that they are equal in terms of merit and reward. Rather, the hadeeth states that the mujaahid is better, because when the Prophet, sallallahu ‘alayhi wa sallam, was asked who is the best among the people, he started his answer with the mujaahid. Then, when he was asked, "Who is next?" meaning who is below him, or after him, in merit, he mentioned the believer who is in one of the mountain paths.

The sentence that you are asking about indicates that the good deed that is right below jihaad in excellence is that a believer secludes himself by not mixing with the people along with adhering to Taqwa (fear of Allah) and refraining from harming others. Al-Haafith Ibn Hajar said, “The believer who isolates himself (from people) is after him (the mujaahid) in merit because the one who mixes with people is not safe from committing sins...” [Fat-h Al-Baari]

The author of ‘Awn Al-Ma‘bood said, "It is deduced from this hadeeth that it is preferable to isolate oneself from people to be safe from backbiting, idle talk, and the like. This preference is restricted to the presence of Fitnah (temptation), but when there is no fear of Fitnah, then the majority of scholars hold that it is better to mix with people."

As for the good acts that lead to Paradise, Allah willing, other than jihaad, then all righteous deeds can be reasons for entering Paradise by the will of Allah. The Islamic Sharia encouraged some of these deeds in particular, such as restraining the tongue and the private parts from committing sins, and underlined that they are among the means of entering Paradise; the Prophet, sallallahu ‘alayhi wa sallam, said, “Whoever guarantees me (the chastity of) what is between his legs (i.e. his private parts) and of what is between his jaws (i.e. his tongue), I guarantee him Paradise.” [Al-Bukhari]

Another of those deeds is to refrain from asking people for money. The Prophet, sallallahu ‘alayhi wa sallam, said, “Whoever can guarantee me one thing, Paradise will be his.” (One of the narrators) Yahya said, ‘Here, a statement which means that he does not ask the people for anything.’” [An-Nasaa'i]

The Prophet, sallallahu ‘alayhi wa sallam, also said, “I guarantee a house in the outskirts of Paradise for a man who gives up arguing even if he were in the right, a house in the middle of Paradise for a man who gives up lying even if he were joking, and a house in the upper part of Paradise for a man who has good manners.” [Abu Daawood]

More deeds have been mentioned in the following statement of the Prophet, sallallahu ‘alayhi wa sallam, “O people, spread the Salaam (the greeting of peace), offer food to people, and pray at night when the people are sleeping, and you will enter Paradise in peace.” [At-Tirmithi]

Allah knows best.