RequiredFieldValidator
asp:TextBox Id="UserName" runat="server" /> /asp:TextBox>* asp:RequiredFieldValidator id="valUserNameRequired" ControlToValidate="UserName" ValidationGroup="Form1" ErrorMessage="UserName is a required field." Display="None" Runat="server">
CompareValidator [password]
asp:TextBox Id="UserName" runat="server" /> /asp:TextBox>* asp:CompareValidator id="valComparePassword" ControlToValidate="ConfirmPassword" ValidationGroup="Form1" ErrorMessage="Password fields must match." ControlToCompare="txtPassword" Display="None" EnableClientScript="true" Runat="server"/>
CompareValidator [date]
asp:TextBox Id="date" runat="server" /> /asp:TextBox>* asp:CompareValidator id="valDate" Type="Date" ControlToValidate="Date" Operator="DataTypeCheck" ValidationGroup="Form1" ErrorMessage="mm/dd/yyyy" Display="None" Runat="server"/>
RegularExpressionValidator [email]
asp:TextBox ID="email" runat="server" ToolTip="you@emailprovider.com"> /asp:TextBox> asp:RegularExpressionValidator ID="valEmail" runat="server" ErrorMessage="Invalid email format!" ValidationGroup="Form1" ControlToValidate="email" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"> /asp:RegularExpressionValidator>
RegularExpressionValidator [phone]
asp:TextBox ID="phone" runat="server" ToolTip="(333) 444-5678"> /asp:TextBox> asp:RegularExpressionValidator ID="valPhone" runat="server" ErrorMessage="(333) 444-5678" ValidationGroup="Form1" ControlToValidate="phone" ValidationExpression="\(\d{3}\) \d{3}\-\d{4}"> /asp:RegularExpressionValidator>
RegularExpressionValidator [date]
asp:TextBox ID="date" runat="server" ToolTip="mm/dd/yyyy"> /asp:TextBox> asp:RegularExpressionValidator ID="valDate" runat="server" ErrorMessage="mm/dd/yyyy" ValidationGroup="Form1" ControlToValidate="date" ValidationExpression="^\d{1,2}/\d{1,2}/\d\d\d\d$"> /asp:RegularExpressionValidator>
RegularExpressionValidator [number]
asp:TextBox ID="user_id" runat="server" ToolTip="06"> /asp:TextBox> asp:RegularExpressionValidator ID="valNumber" runat="server" ErrorMessage="Numbers only" ValidationGroup="Form1" ControlToValidate="user_id" ValidationExpression="^\d+$"> /asp:RegularExpressionValidator>
RegularExpressionValidator [number, 2 decimals]
asp:TextBox ID="amount" runat="server" ToolTip="34.56"> /asp:TextBox> asp:RegularExpressionValidator ID="valAmoun" runat="server" ErrorMessage="Two decimals number" ValidationGroup="Form1" ControlToValidate="amount" ValidationExpression="^\d*\.\d{2}$"> /asp:RegularExpressionValidator>
Regular ExpressionValidator [username, exact lenght ]
asp:RegularExpressionValidator ID="InputLenghtDefined" runat="server" display="dynamic" ControlToValidate="usnCheck" ErrorMessage="Username must be one word 4 - 20 characters!" ValidationExpression="[^\s]{4,20}" /> /asp:RegularExpressionValidator>
Once you drag RegularExpressionValidator on the “Designer”, in design view select the Requarexpressioncvalidator control. In “Properties” on the right-hand side there is a ValidationExpression field. Select expression that you would like to use from a list of expressions provided by .NET. Once you choose the expression you want there is a Validation expression: textbox that holds the regex used for the validator.
See some examples on Microsoft Support website (KB316662), or better yet this this source.