A great little book on Spinoza is Deleuze's Spinoza: Practical Philosophy. He find within Spinoza many similarities to Nietzsche; in fact, the latter philosopher's name is the very first word in the book.
Deleuze sees both Spinoza and Nietzsche as philosophers who saw the world in terms of power relations. For both, joy is the increase in one's perfection. They are both naturalists in their ethics: for both, joy (goodness) is whatever aids one's power to act, to feel, and to think, whereas sadness (badness) is whatever injures one or prevents one from acting, feeling, and thinking. Deleuze calls them philosopher of "immanence", a concept that Deleuze made central to his own system.
There are many similarities between Spinoza's concept of the conatus and Nietzsche's Will to Power. They both connote the vital impulse in living beings to pursue in existence, and to seek their own advantage. However, Nietzsche emphasized that the Will to Power is a blind striving towards domination and mastery of the external world, an attribute which he felt Spinoza did not emphasize enough.
There are differences between the two, however. While Spinoza affirmed that in political matters might makes right, he felt that the highest form of the power of society is in democracy. He advocated for democracy from a philosophical perspective long before Locke did. Nietzsche on the other hand was more cynical about democracy, and emphasized the differences between the noble and lower classes, occasionally suggesting that society ought to be divided between those lines, lest excellence in culture and intelligence be eroded by the conformism of the lower classes.
The biggest difference was philosophical method: Spinoza was a rationalist metaphysician, and wrote his magnum opus Ethics in proposition form. He desired to demonstrate his naturalism with rational argument. Nietzsche on the other hand took his arguments from an philological/historical method that he called a "genealogy" of morality. He felt it was important to understand exactly how the moral concepts of Good and Evil developed in the Western world. He saw them developing out of Platonic philosophy and the rise of Judeo-Christianity (the latter religion being a form of Platonism). Nietzsche felt it was necessary to know how values changed through history so that we may be capable of destroying all transcendent values that posit a future "better world" (whether that be the heaven of Christianity or the techno-utopia sought after by scientists, engineers, and social reformers) in favor of earthly values based on life. Earthy values are ones that aid in one's power to act.
Deleuze, for his part (and how I see it), felt that these earthly values need not amount to a glorification of men dominating other men, but of man 'dominating' the world. The will to power can, for instance, be the mastery of a painter over color, or of a scientist over phenomena. That's why the will to power is ultimately a force of creation, because true mastery expresses the power that one has, whereas destruction shows only the power that one lacks. To create values increases our power in terms of other powers that we possess, whereas to simply destroy values expresses only a feral, powerless desire to gain powers that we don't already have.
