Default button

Filling in forms by only using keyboard commands is very popular and should get more attention than most developers give it.
I have seen a lot of weird JavaScript functions in a WebForms page to fake a button click when a user presses the enter button.
This is really unnecessary. There is a nice feature which allows you to set the submit button for a (sub)section of a WebForms page.
Every container element (f.e. Panel) supports this feature. Pressing enter on any focusable element will trigger a click on the button defined by the DefaultButton property of the parent container element.

<asp:Panel ID="pnlFormName" runat="server" DefaultButton="btnSubmit">
    <asp:TextBox ID="txtName" runat="server" />
    <asp:TextBox ID="txtMiddleName" runat="server" />
    <asp:TextBox ID="txtLastName" runat="server" />
    <asp:Button ID="btnSubmit" runat="server" />

Tab order

Another thing to keep in mind is the tab order. The order can be set by setting the TabIndex property of an HTML Input element (or any other element which should be focusable).
The default tab order will fit most cases; it is equal to the positioning order of the elements.

<asp:Panel ID="pnlFormName" runat="server">
    <asp:TextBox ID="txtName" runat="server" TabIndex="1" />
    <asp:TextBox ID="txtMiddleName" runat="server" TabIndex="2" />
    <asp:TextBox ID="txtLastName" runat="server" TabIndex="3" />
    <asp:Button ID="btnSubmit" runat="server" />