Common words:
* swap
* swam
* swan
* swarm
* swat
* swear
* sweat
* sweep
* sweet
* swell
* swift
* swim
* swing
Less common words:
* sward (grassy ground)
* swathe (wrap or bind)
* swain (young man, especially a lover)
* sway
* swearword
* swill (drink greedily)
* swine
* swirl
* swoon
* swoop
* swarthy (dark-skinned)
Proper nouns:
* Swaziland (a country in Southern Africa)
* Swahili (a language spoken in East Africa)
This is not an exhaustive list, but it should give you a good starting point. You can also use a dictionary or online thesaurus to find more words that begin with "swa".