First of all, condition is everything and if the records are scratched or worn, they are worth very little unless they are really rare.
If however they are in reasonable nick, then a good idea is to check internet auction sites to see what sort of prices similar records are fetching (search on labels/artists). If the prices are worthwhile, consider selling in same way. If not worth it, then charity shops are always pleased to receive your donations. There are always people searching through boxes of 45s in my local shops!
The lack of a cover (on a single) is not necessarily a disaster, though of course the record can get scratched. In fact, many DJs replace the ordinary paper cover with a card cover for their racks, since the paper cover would deteriorate very quickly in use.
There are firms which sell plain paper or card covers for records of all shapes and sizes, if the records are good enough to warrant it.