You can narrow your search by genre etc, there are new free ones all the time but many of them don't stay free for more than a day or two at a time so download them when you see them. You click from here to amazon to buy.
Some free ones that I enjoyed but wouldn't have read in a paperback where people could see my shameful reading material:
Ok. Have new kindle fire, need suggestions for adult fiction please that I don't need to admit to people I have bought! Two young children so need to kickstart our SEX life! (Likes the romance of fifty shades but the sex left me neutral!)