Honokowai Beach Park is a personal favorite. It's located right next to the Aston Paki Maui Resort and across from the Lahuiokalani Chapel.
The park has a recently upgraded playground and bathroom/shower facility. There are barbecue grills, picnic tables and a large grassy area with lots of shade. There are usually parking spots available.
The park is a very popular gathering spot for locals after work and on weekends.
The beach itself is extremely narrow and rocky near shore. If you wade down to the Paki Maui Resort, there's an opening through the coral to an area where you can swim between the two reefs. It's well protected, generally calm and the snorkeling is excellent.