Looking for good reference book in molecular biology
These always have a place at my library

HF Lodish, Berk, Arnold, and S. Lawrence Zipursky. Molecular cell biology. Vol. 4. New York: WH Freeman, 2000.

Alberts, Bruce, et al. "Molecular biology of the cell." Garland Science, New York 4 (2002)(the first few editions had James Watson himself as the editor)

Brown, Terence A. Genomes. Garland science, 2006.

For basics. I would recommend staring with Brown, and going on to Bruce Alberts and then Lodish. That's the way I learnt it.

For a really nice book with pictures (yes, we all like those) you might want to look into Lippincotts illustrated reviews (biochemistry, cell and molecular biology and the like). They are also quite good.

For a specific emphasis on techniques, I'd  recommend this:

Sambrook, Joseph, Edward F. Fritsch, and Tom Maniatis. Molecular cloning. Vol. 1. No. 7.58. New York: Cold spring harbor laboratory press, 1989.
(You can read the contents here http://www.molecularcloning.com/)