Lang's "Algebra" is without doubt one of the classic references but sticking to it, or to only one book for that matter, depends highly on your style tastes, background level and aim. A beginner in abstract algebra may find the exercises in Lang to be too hard or/and to leave important concepts and results as problems.
You should check out other standard references listed below, and see their style to decide which suits you best:
- Dummit; Foote - "Abstract Algebra", Wiley 2004.
- Rotman - "Advanced Modern Algebra", AMS 2011.
- Hungerford - "Algebra", Springer 1974 (2003).
- Grillet - "Abstract Algebra", Springer 2007.
The first is the standard title used in many American graduate schools for the preliminary/qualifying examination in graduate algebra, although many people would consider it an upper undergraduate book. It is filled with lots of exercises and examples. The third book is very abstract and general, encyclopedic and good as a reference since it is highly formally organized with just definitions-theorems-proofs-corollaries, with a great selection of exercises (I think better than Lang's); but, although it covers with great generality topics the others take longer to explain, it lacks chapters on homological algebra or representations, which the others have. Finally the second book is a mixture of all styles, and in particular is my favourite. It is the biggest, with around 1000 pages, it has an informal style in its explanations but a highly rigorous development, with insightful examples and filled also with lots of exercises (which I particularly find well-suited for self-study). The last one is a quite recent textbook which some people will detest while others will love.
There are many other abstract algebra titles, this is just a small standard selection. Although many consider Lang to be better, do not forget that it is always best to learn from at least two different sources, so that you can clarify dark passages of one in the other, fill complementary material or provide easier examples/exercises to start with.
Once you have mastered the standard graduate course, or if you want to deepen your knowledge on particular chapters of the previous books, like commutative algebra for example as requisite for algebraic geometry, you may jump to the next level of more specialized texts:
- Roman - "Advanced Linear Algebra", Springer 2008.
- Fulton; Harris - "Representation Theory, A First Course", Springer 1991.
- Eisenbud - "Commutative Algebra with a View toward Algebraic Geometry", Springer.
- Singh - "Basic Commutative Algebra", World Scientific 2011.
- Matsumura - "Commutative Ring Theory", AMS 2011.
- Rotman - "An Introduction to Homological Algebra", Springer 2009.
- Weibel - "An Introduction to Homological Algebra", Cambridge U. Press 1994.