You can use the MembershipProvider.GetAllUsers Method:

int total;
var users = mbr.GetAllUsers(0, int.MaxValue, out total);

or pass an index and page size if you have a paging grid.

And here an ASPX fragment defining the gridview:

<asp:GridView runat="server" ID="GV"></asp:GridView>

And the corresponding code-behind C# class:

public partial class MyPage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // create membership instance...
        int total;
        GV.DataSource = mbr.GetAllUsers(0, int.MaxValue, out total);
        GV.DataBind();
    }
}