Notre-Dame de Paris:

The significant theme of fate in "Notre-Dame de Paris" is strongly ennumerated in several ways: the general trend towards fatalism in plot and character (especially Frollo) and the motif of the fly in the spider web, strongly smelling of fate, but moreso interpereted as the fly caught on a journey towards a light, or freedom. This image so skillfully displays in the truest Hugoesque style this particular struggle of man, desperately battling against the three strongest problems(as I think he discussed in the introduction to "Les Travaillers de la Mer"["The Toilers of the Sea"]) which are superstition (namely of the church), misery placed upon man by society, and the helplessness of man before nature.
Another significant motif is that of stone and upturned pavement. Quasimodo is frequently compared to his stone gargoyle companions and architectural terms are used in his descriptions (spiral legs, and a dome on his back, also more relating him to the cathedral), and Frollo is shown as an animated statue. Upturned pavement and stone in general was a powerful symbol in Hugo's mind for the process of change, and that grand efficy that change leaves behind. Hugo could not escape the idea of revolt, hence the thieves storming Notre-Dame.
And this brings us to a phenomenally important idea not only in "Notre-Dame de Paris" but all of Hugo's works, even the more obscure ones; that is to say, the process, need, and result of change. Hugo felt a great affinity for the ocean, and, itself being a grand redeemer of change, would perhaps illustrate my point most clearly. From its depths, life springs forth; the ocean is mother to life on Earth, but contrastly its ebb and flow, its rushing torrents and massive waves, its great salt spray has an incredible destructive force: the ability to tear down great rock pinnicles and swallow men, even ships, whole. This is the enigma Hugo faced, the absolute need for change weighed with its destructive capabilities. He shows this in "Notre-Dame de Paris", after telling a thrilling story far more dramatic than any that would happen to us,with the disintigration of Quasimodo's bones into dust. The last testament to this grand story is gone, with the exception of one marking: Frollo's somber carving of the word "Fate" into a wall of the cathedral.
Despite the fact that in the introduction Hugo says that the inscription has long since been plastered over, the idea remains of the supreme power of the word. In the chapter entitled "This Will Kill That," Hugo explains the power of Gutenberg's invention , and that the only means for expression before the printing press was architecture. Indeed whereas Hugo believed the French Revolution to be the single most important event since the coming of Christ, he regarded Gutenberg's printing press as "la mere revolution."
Also observe some subtle imagery of which I once read about. Esmeralda, throughout the book, is associated with water; where ever she is, there is sure to be water nearby (the water she gives to Quasimodo and Gringoire's fall into a gutter after following her are two examples), while Quasimodo is very much associated with the sun and fire: his red hair being the most obvious example. All this, I believe, leads to Hugo's incredible control over antithesis, very much an integral part of the book, whose facets and examples are so numerous, I don't see the need to mention them.

Les Miserables:

The main motifs in "Les Miserables" are that of change(revolution), redemption, and a particular theme of salvation from below.
Redemption, the word itself, comes from the latin to buy back, so it is no coincidence that most of the major plot developments are surrounded by, or simply based on, money. The bishop gives Valjean the candlesticks with the morose statement that he is buying his soul for God. Valjean saves young Cosette from the clutches of the Thenardiers only through use of money. Even during Valjean's deathbed scene, mentions of his will and its heirs are not scarce (there may be something more in the fact that Marius refuses Valjean's money until he is convinced that he earned it honorably). Indeed, money is one of the most frequent and penetrating images in the novel.
The barricade incident stands testament to Hugo's firm belief in the urgent need for change. It may seem strange to some that Hugo tends to glorify the horrors that take place in insurrection, an idea that Hugo himself battled with and confronted in his novel, "Quatre-Vingt Treize"("Ninety-Three"), but symbolically, it all leads up to the grand idea of revolution, and ultimately, change. The idea of salvation from below is ennumerated several times in the book, namely in Valjean's sanctuary in the convent and his descent into the sewers with Marius. Whereas the convent is described as a place where the sins of others are atoned for, a place often described as one of filth, the sewers are not much different; the sewers are a cesspool of filth, the convent one of sin. These images merely attest to the idea that salvation, religious and social, shall arrive from the lowest strata of society, maybe best illustrated by Gavroche. The motif of excrement also appears in Hugo's long Waterloo section where Cambronne utters the phrase, "Merde!"("Shit!"), but as I lack the time, I shall reserve my desire to discuss Waterloo.

Quatre-Vingt Treize:

I am running short on time, so let me be brief. Consider how "Quatre-Vingt Treize" begins and ends on highly ironic tones; that is amidst the grandeur, glory, and sheer beauty of nature, the destruction and blood of man penetrates. Also, throughout the book, Gauvain is described with feminine features, especially his long effeminate neck. As far as I can tell, and I have had little time to ponder on this book, these ironies and contrasts display Hugo's overall ambivalence toward the horrors and blessings of Revolution, and also the primary antithetic characteristic of Nature (I recall a chapter whose title was "Totus in Antithesi", whose matter may reveal much more). Indeed, on one level, the escaped cannon in the ship's hull and the act of the three children tearing up the book in the library where they are held prisoner certainly represent the destructive forces of Revolution, although I once read that the subject of the book they wear tearing was the Saint Bartholomew's Day Massacre, and that correlates somewhat, but I have forgotten how.
But in my view, the most interesting aspect of the book is its depiction of a cyclical, in contrast to a linear, history. Recall how the book and ends on the same ironic note: Forgoing my earlier examples, whose point reveals its relevance as well,the sergeant, at the beginning, sheds a tear as he looks upon the children, and the forces all cry at Gauvain's execution. I believe Hugo, even at this time, had a strong belief in fate, and whereas a linear history bends more towards the idea of free will, a cyclical history tends to imply an overhanging fate.

I hope these points can help out with analysis of Hugo's works. Of course there is so much more in his novels than written here, so many levels, antithesis, symbolism, and inherent unity that perhaps some day I will try to delve more deeply into. If you are interested in further learning about Hugo in this regard, I have read a truly excellent book which discusses his major novels and does a fine and thorough job of analysing them. It is called "Victor Hugo and the Visionary Novel" by Victor Brombert. It is from this book from which I have extracted most of my knowledge about Hugo's works, so check it out if you get a chance.