1. You will need to use jQuery
2. You need to place all controls in a DIV with class controls as I did
3. You need to give all controls a CssClass Tab
 
    <form id="form1" runat="server">
    <div class = "controls">
        <asp:TextBox ID="TextBox1" CssClass="Tab" runat="server"></asp:TextBox>
        <asp:TextBox ID="TextBox2" runat="server" CssClass="Tab"></asp:TextBox>
        <asp:DropDownList ID="DropDownList1" CssClass="Tab" runat="server">
            <asp:ListItem Text="1" Value="1"></asp:ListItem>
            <asp:ListItem Text="2" Value="2"></asp:ListItem>
        </asp:DropDownList>
        <asp:RadioButtonList ID="RadioButtonList1" CssClass="Tab" runat="server">
            <asp:ListItem Text="1" Value="1"></asp:ListItem>
            <asp:ListItem Text="2" Value="2"></asp:ListItem>
        </asp:RadioButtonList>
        <asp:TextBox ID="TextBox3" CssClass="Tab" runat="server"></asp:TextBox>
        <asp:Button ID="Button1" CssClass="Tab" runat="server" Text="Button" />
        </div>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type="text/javascript">
        $(".Tab").on("keypress", function (e) {
            if (e.keyCode == 13) {
                var index = $(this).index();
                var next = $(".Tab", $(this).closest(".controls")).eq(index + 1);
                if (next.length > 0) {
                    if (next[0].tagName == "TABLE") {
                        $("input", next).eq(0).focus();
                    } else {
                        next.focus();
                    }
                } else {
                    next = $(".Tab", $(this).closest(".controls")).eq(0);
                    next.focus();
                }
                return false;
            }
        })
    </script>
    </form>