Basically you need the documents to provide the evidences that you are studying well and have enough financial sources. As far I remember when I sent documents to apply for wife, the required documents are

1. Original I-20 with your wife's CORRECT NAME as appear in the passport.

2. Letter from department and professor to demonstrate you are making progress towards the degree.

3. Do you have teachinh assistantship or research assistantship? if yes, request to include in the department letter or advisor's letter and amount.

4. Your recent transcript and course registration for the coming semester.

5. In I-20 if you do not have financial assistantship enough to cover the expenses after your wife gets here, you also need to include bank statement showing your personal asset to support her.

From Nepal,

1. Application with copy of I-20, and all documents you sent.

2. Married certificate

3. Are you newly married?, she may also need to take few photoes taken with you.

4. If you have enough financial support, she does not need to show any other evidence in Nepal.

I think these are all. Hope other friends add more if I missed something.

Good luck.