Robespierre is one of those historical figures subject to enormous biographical scrutiny. As such, there are plenty of 'good books' on him; but I'll assume you mean those that are easily procurable, and in English. If you do read French, though, that's an added bonus and I could suggest a few recent French works that bring great value to the debate over his life.

Otherwise, the most recent English biography is by Peter McPhee (Robespierre: A Revolutionary Life, 2012), who stresses Robespierre's earlier life and distances himself from the psychoanalytical lenses of many (often French) former works, which read Robespierre's youth without a mother and with a negligent father as symptomatic or preconditions for his future. It's a strong return to the more human side of a figure who's been frequently either mythologised or demonised by the left and right respectively. See in counterpoint Ruth Scurr's Fatal Purity: Robespierre and the French Revolution (2006), which is quite dominant in most book stores and the like due to its good publication timing in the English market almost a decade ago now, and which takes the tag of 'l'Incorruptible' very seriously, introducing criticisms through that prism. The classic Robespierre and the French Revolution (1935) by the British historian J.M. Thompson is still regarded very highly amongst contemporary scholars, even if occasionally coloured by his Anglican past. But those instances are intermittent and don't reduce the beauty of his prose and insightful portrayal of Robespierre. The late Norman Hampson's The Life and Opinions of Maximilien Robespierre (1974) also remains something of a curious landmark in the field for its innovation: less a biography than a constructed dialogue, around which Hampson's understanding of Robespierre emerges through the four interlocutors, its structure doesn't dull the potency of its interpretative force - in fact, it rather supports it, I think. Then there are other biographies, e.g. Hardman, Rudé, and so forth.

I answered a question a while back on Robespierre from a more source-based perspective; if that interests you, have a look at https://www.reddit.com/r/AskHistorians/comments/320u36/having_trouble_finding_primary_sources_from/cq79bij.