Basic words:
* Salut (hello)
* S'il vous plaît (please)
* Si (if)
* Surtout (especially)
* Seulement (only)
* Suite (following)
* Soit (either)
* Sans (without)
* Savon (soap)
* Sac (bag)
* Soleil (sun)
* Salle (room)
* Sœur (sister)
* Son (his/her)
* Sentir (to feel)
* Sourire (to smile)
* Super (great)
Food and drink:
* Salade (salad)
* Sauce (sauce)
* Salade (salad)
* Soupe (soup)
* Spaghettis (spaghetti)
* Sucré (sweet)
* Salade de fruits (fruit salad)
Places and things:
* Salle de bain (bathroom)
* Salon (living room)
* Secrétaire (secretary)
* Style (style)
* Sable (sand)
* Sentier (path)
* Soirée (evening)
* Station (station)
* Statue (statue)
* Sieste (nap)
Verbs:
* Savoir (to know)
* Sortir (to go out)
* Servir (to serve)
* Souhaiter (to wish)
* S'asseoir (to sit down)
* Se coucher (to go to bed)
This is just a small selection, and there are many other common French words starting with "s."