Getting non string values from the querystring can be a chore if you need to read alot of values; parsing to the required type and ensuring the querystring value doesn't cause an exception ("adsf" cannot become an integer) can add alot of code to each page. So a long while ago I created a small helper class to do this for me, which I've now upgraded (after reading a blog entry by ScottH about TypeConverters) to use generics and extension methods. I've also included methods to get a value from the Request.Form property.

using System;
using System.Web;
using System.ComponentModel;

namespace LukeSmith.Web
{
    public static class HttpRequestHelper
    {
        public static T? GetQueryValue<T>(this HttpRequest request, string name)
            where T : struct
        {
            return ConvertFromString<T>(request.QueryString[name]);
        }

        public static T? GetQueryValue<T>(this HttpRequest request, int index)
            where T : struct
        {
            return ConvertFromString<T>(request.QueryString[index]);
        }

        public static T? GetFormValue<T>(this HttpRequest request, string name)
            where T : struct
        {
            return ConvertFromString<T>(request.Form[name]);
        }

        public static T? GetFormValue<T>(this HttpRequest request, int index)
            where T : struct
        {
            return ConvertFromString<T>(request.Form[index]);
        }

        private static T? ConvertFromString<T>(string value)
            where T : struct
        {
            T? result = null;

            if (!string.IsNullOrEmpty(value))
            {
                TypeConverter converter = TypeDescriptor.GetConverter(typeof(T));

                if (converter.CanConvertFrom(typeof(string)))
                {
                    try
                    {
                        object obj = converter.ConvertFromInvariantString(value);
                        result = (T)obj;
                    }
                    catch (Exception)
                    {
                    }
                }
            }

            return result;
        }
    }
}

Updated: Why Try/Catch was used