Just simple jQuery form input validation plugin witch uses regular expressions for validations. Main different from others validations plugins that this plugins does validate in real time.

Plugin code:
 

jQuery.fn.rval = function(regExp)
{
	regularExpression = regExp;
	valueCurrent = "";
	blockInput = false;
			
	this.keypress(function(e){
	    if (blockInput == false)
		{
		      valueCurrent = this.value;
		      blockInput = true;
		}
	})
	
	this.keyup(
		function(e)
		{		   
		    instance = this;
		    var allOk = false;		    
		    $.each(
            regularExpression,
            function( intIndex, objValue ){ 
                    var re = new RegExp(objValue);                                        
        			if((re.exec(instance.value) || instance.value == '') && allOk == false)
        			{
        			    allOk = true;        			    		    
        			} 
                 }
            );            
            if (allOk != true) {
        			     instance.value = valueCurrent;	
        	}        			 
            blockInput = false; 
		}
	)
	
	return this;
}

Plugin can be called using syntax like this.

$("#only_int_float").rval([/^([0-9]{0,6})$/,/^[0-9]{1,6}[\.|,]{1}(|[0-9]{0,2})$/]);

In example above i accept only integer and float numbers. Decimal part can be separated by "," or by ".".
Example: http://remdex.info/examples/validator/index.html