"Ngh," "Mmm," "Uhn," "Ugh," "Mmmph," "Mph," "Ooh," "Ahh," "Eeee," "Nnn," "Ggggh," "Hnnng," "Unh," "Mmmh," "Oomph." These are basic building blocks. To expand on these, consider adding:

• Intensity: A simple "Ngh" can become a drawn-out "Nnnnnnngghhhh" for increased intensity, or a short, sharp "Ngh!" for a sudden burst of sound. Experiment with the length and volume of the sound.

• Pitch: Vary the pitch to convey different emotions. A higher pitch might suggest pain or pleasure, while a lower pitch could indicate exertion or deep satisfaction.

• Breathiness: Add breathiness to the sound by adding a slight "h" sound at the beginning or end, or by making the sound slightly airy. For example, "Hngh," "Nghh," or "Mmmh."

• Throatiness: A throatier sound can be achieved by adding a guttural quality, almost like a growl. This can be achieved by focusing the sound in the back of the throat. Examples include "Ggggh" or "Hnnng."

• Nasality: Adding nasality can create a different texture. Try adding an "m" or "n" sound to the beginning or end, or by letting the sound resonate in your nasal passages. For example, "Mngh" or "Nngh."

• Combination: Combine these elements to create more complex and nuanced moaning sounds. For example, a breathy, high-pitched "Mmmh" could convey a different emotion than a throaty, low-pitched "Ggggh."

• Contextual Clues: Don't rely solely on the sound itself. Use surrounding descriptions to enhance the reader's understanding. For example, instead of just writing "Ngh," you could write "A low, throaty 'Ngh' escaped her lips as she arched her back."

Remember to consider the context of your writing. The type of moan will vary greatly depending on the situation and the character's emotional state. Experiment and find what works best for your story.