tell some best and simple editor names like (FCK editor , WMD editor) (For inside textare field)
Note that FCKEditor is now CKEditor.
TinyMCE is another major, full-featured editor. Both CKEditor and TinyMCE are quite heavyweight, though -- they both provide large and robust platforms for integration, which isn't always what you want. That said, they are easy to customize and are actively developed, with wide support for different browsers.
Both editors allow you to customize the toolbar to display only the buttons you want.
Also, for image uploading, CKEditor has CKFinder (see the demo) and TinyMCE has a number of third-party projects that add image uploading, such as TinyBrowser.
TinyMCE is the best i've ever used, but if you use jQuery and you want a simple editor try jHTMLArea
Personally I've found NicEdit to be quite good.
update: From the OP's comment it seems his current use of Nicedit does not have a vertical scroll bar. For that, simply limit the height of the textarea:
<style>
#editableContent {
height : 20em; /* this is the key */
}
</style>
<form>
<textarea id="editableContent" name="editableContent"></textarea>
</form>
<script>
var ed = new nicEditor();
ed.panelInstance('editableContent');
</script>