Firstly the theme tunes, which are awesome in every game; outside of Legend, they are all based off the same Leitmotif, but each manages a very distinct flavour:
Tomb Raider I. The purest, most iconic form of the series' motif, played on solo flute against a tranquil background medley of harps and choir.
Tomb Raider II. This one manages to blend in Asian elements to the main theme, while introducing several counter-motifs that turn up in future games as well. Note, especially, the soothing piano line.
Tomb Raider: The Last Revelation. The melancholy theme, backed by a lone xylophone, immediately foreshadows the game's darker premise.
Tomb Raider Chronicles doesn't have a single theme, but pieces together four mini-themes, two of which are simply lifted from TR1 and TR4. The remaining two: Titles Flyby 1, and Titles Flyby 2. Both are excellent companions to the on-screen images of Lara's mansion in the rain and her parents praying in the chapel, respectively.
Angel of Darkness. The full orchestration works wonders on this hauntingly beautiful, mournful song.
Legend. A symbol of Lara's return to form. It even samples the traditional Gaelic folk song, "Ailein duinn", to powerful effect.
Anniversary. A return to the simplicity of the first game's theme, but with more depth and mystery.
Underworld. A slightly sad and very epic theme that builds to a choir-heavy crescendo, then softly closes with the iconic motif.
An amazing atmosphere track. Music is reduced almost entirely to short cues in the first game, and yet when entering a massive Egyptian complex, this long track of music starts to play, further enhancing the feeling of grandeur.
An ambush theme most famous for its use in the T. rex fight. Just like the dinosaur, the sudden, fast paced and tense melody comes out of nowhere, greatly adding to the moment and making already tough fight all that more intense.
Venice Violins. A gorgeous violin-only piece that plays during the boating segments of Venice, and it simultaneously gets the blood pumping and brings to mind a cruise through the canals.
A jungle theme. It starts and fades into jungle sounds, but the most important is the rhythmic sitar and tabla music. It's matched with entering mysterious jungle and building the atmosphere, but also perfectly timed with fighting with the first tiger in the game, fading out soon after the predator is killed.
Track from Croft Manor. It's infamously spooky (and intentionally played a bit too loud in the Croft Manor), matching the theme of searching for puzzles and hidden passages spread all over the building.
Ambush theme. Just like the name implies, it greatly adds to sudden ambushes, forcing players to think on their feet and either run away or facing danger head-on.
A boss theme. It plays for the first time when Lara faces an immortal enemy and the music nicely conveys the feeling of being caught in a hapless struggle.
Jeep Thrills Max plays when Lara needs to chase down some bad guys across the desert in her jeep. As the name implies, the track is thrilling from start to end.
Rise of the Tomb Raider: "I Shall Rise" by Karen O. A slow building, triumphant credits song that really shows how much this Lara has grown and overcome all that life's put in her way.
. The purest, most iconic form of the series' motif, played on solo flute against a tranquil background medley of harps and choir.