Fabrics
Felt: It is a non-woven fabric. Commonly used by beginners because it’s extremely cheap and also has no stretch whatsoever.
Cotton: Often used in older soft toys, but has fallen out of style because it’s not soft, isn’t stretchy and frays if you don’t treat it correctly.
Faux suede: This is the standard go-to when you want a soft, but not “fuzzy” texture, like in skin or clothing. Most faux suede is not stretchy.
Fleece: This is fabric made from knitting fibers. Recommended as one of the better fabrics for beginners because it’s soft, fairly inexpensive, is stretchy and forgiving when you make mistakes.
Minky: Another fabric made from knitting fibers, this means it is stretchy. Probably the most popular fabric for soft toys. It’s extremely soft, has a fluffy but smooth texture and is fairly easy to work with. The downside to minky is that it’s more expensive than other types of fabric for soft toys.
Faux fur: It is extremely thick, difficult to work with and not stretchy at all, so making entire plush with it is rather difficult. The upside to faux fur is that the fluffiness of it tends to hide mistakes in sewing. This fabric is also expensive compared to other types.
This link has great information about pros and cons of different types of fabric for soft toys.
Stuffing
Polyfil: relatively inexpensive polyester-based filling. When put inside a stuffed toy, polyfil also known as polyester fiberfill will hold its shape perfectly
Cluster Stuff: More expensive than polyfil, but the fibers don’t clump the same way polyfil does, so plush stuffed with it tend to be softer and squishier.
Natural pellets and dried herbs: If you want to go all-natural while still maintaining the pellet feel, you can use beans, rice, and other natural herbs. You can create a potpourri or scented soft toy, stuff a pouch with dried herbs and surround it with other filling.
Shredded memory foam: Not good for every project, but has specific applications.
Micro-beads: These are like a tiny version of what’s in beanbag chairs
Poly pellets: Not usual, but it is used to add weight to plush. These pellets are hard plastic pellets. Generally is used in conjunction with a fiber stuffing to not make the soft toy too heavy.