Sharepoint - Create multiple items via REST API

Unfortunately, the REST API does not provide a way to batch items (yet). However, you can batch add items using the JavaScript Client Object Model. Here is a sample code:

var itemArray = [];

function createListItems() {

    var clientContext = SP.ClientContext.get_current();
    var oList = clientContext.get_web().get_lists().getByTitle('TestList');


    for(var i = 0; i< 5; i++){

        var itemCreateInfo = new SP.ListItemCreationInformation();
        var oListItem = oList.addItem(itemCreateInfo);  
        oListItem.set_item('Title', 'My New Item!' + i);  
        oListItem.update();
        itemArray[i] = oListItem;
        clientContext.load(itemArray[i]);
    }

    clientContext.executeQueryAsync(onQuerySucceeded, onQueryFailed);
}

function onQuerySucceeded() {

    alert('Items created');
    alert(itemArray[0].get_id());
    alert(itemArray[0].get_item("Title"));
}

function onQueryFailed(sender, args) {

    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

createListItems();

Update

REST API supports batching now:

https://dev.office.com/sharepoint/docs/sp-add-ins/make-batch-requests-with-the-rest-apis

http://www.vrdmn.com/2016/06/sharepoint-online-get-userprofile.html

Batching is now supported in REST O365 only. You can check out a javascript library on GitHub that batches these for you using the new capabilities.

https://github.com/SteveCurran/sp-rest-batch-execution