Hey mandeep,
Here i am suggesting some good books for UG NET computer science
1. Discrete structures - Seymour lipschutz
2. Introduction to automata theory, language and computation -john E.hopcroft and ullman
3. Programming in C - byron Gottfried
4. OOPS using c++ - E. balagurusamy
5. Digital logic and computer design - M. Morris mano
6. Data structures - Seymour Lipschutz
7. Fundamental of database systems -Ramez Elmasri ,Navathe
8. Data management -GV post
9. Computer networks -Andrew S. Tanenbaum
10. Data and computer communications - William stallings
11. Compilers - principles ,techniques and tools -Aho ,lam, sethi and ullman
12. Operating systems internals and design principles - William stalking
13. Unix - concepts and applications -M.J,back ,S.das
14. Artificial intelligence - Elaine rich and kevin Knight
15 . Software engineering concepts - richard fairley
These books cover whole syllabus of UGNET .
I wish good luck!