Starbound's instruments can be a powerful tool in the right hands, but they take some effort to get working. For one thing, you need the ABC notation of your chosen song. And even then, you have to actually find an instrument out in the universe. Alternatively, you can install Mighty Music, and gain access to hundreds of notations and a selection of new instantly-available instruments.
The pack contains over 2,000 song covers, taken from a variety of games, movies, TV shows and anime. As for instruments, you'll find new synths, drums and, for some reason, a can of beans.
Starbound already has a nice selection of dungeons—randomly generated structures containing hostile creatures and the promise of loot. Still, a bit more variety can't hurt; or, more accurately, it can hurt, but will nonetheless offer some enjoyable challenges along the way. That's what Dungeoneer Dungeons aims to provide. It adds a series of possible dungeon spawns, both large and small. With it, you can find everything from a single caged mini-boss, to a sprawling and extremely difficult military base. It also adds a volcano, which in the creators own words is, "not actually a dungeon, just a giant fucking volcano".
Your Starbound Crew
Vanilla Starbound has basic NPC spawners, but if you really want your ship to feel alive, download this. It adds a full crew to your space voyage, each with a different role and offering a different set of services. More than that, though, each crew member must first be rescued through a custom-made dungeon quest. These quests begin after defeating Dreadwing in the basic tutorial, and so provide a compelling reason to continue on your adventure.
NB: due to the new 'universe' files added by this mod, it is incompatible with the Starbound Mod Manager and must be manually installed.
Variety is the spice of the Universe
The clue is in the title: while Starbound has a decent number of biomes by default, Variety is the spice of the Universe adds many, many more. In all there are more than 50 new planet types, along with new weather effects and even new songs in each biome. It also vastly increases the number of airless planets—meaning you'll need to craft a Survival System to fully appreciate its worlds.
NB: due to the nature of its biome changes, this mod has many potential conflicts. Check this compatibility list for a rough guide as to what will and won't work.
Finally, you can bring some more colour into your worlds with the Dye Pack. Through a new Dye Station terminal, you can customise the colour of nearly any item or material in the game. The mod supports not only the base game's armour, clothing, weapons, objects and blocks, but also that of a wide variety of other mods—including many of the items from the Pixel Goods Store.
In addition, the mod is multiplayer friendly. There's even a special Vanilla Compatible Server Edition, allowing server owners to implement the Dye Pack's functionality without the need for visitors to download it themselves.