Rich's handy C# Extension Methods

ConnectionStringSettingsCollectionExtensions.cs

// ReSharper disable CheckNamespace
namespace System.Configuration
// ReSharper restore CheckNamespace
{
    public static class ConnectionStringSettingsCollectionExtensions
    {
        // Connection strings by default just return null. We want something 
        // a bit more snappy.
        public static string GetOrThrow(this ConnectionStringSettingsCollection connectionStrings, string name)
        {
            if (String.IsNullOrWhiteSpace(name)) throw new ArgumentException("name was null or empty.", "name");

            var connectionString = connectionStrings[name];
            if (connectionString == null)
                throw new Exception(String.Format("The connection string '{0}' was not found.", name));

            return connectionString.ConnectionString;
        }
    }
}

DateTimeExtensions.cs

// ReSharper disable CheckNamespace
namespace System
// ReSharper restore CheckNamespace
{
    public static class DateTimeExtensions
    {
        public static bool IsWeekend(this DateTime date)
        {
            return (date.DayOfWeek == DayOfWeek.Saturday || date.DayOfWeek == DayOfWeek.Sunday);
        }

        public static Guid ToDeterministicGuid(this DateTime date)
        {
            var str = String.Format("{0:yyyyMMdd-HHmm-00ss-ffff}-000000000000", date);
            return Guid.Parse(str);
        }
    }
}

EnumeratorExtensions.cs

// ReSharper disable CheckNamespace
namespace System.Collections.Generic
// ReSharper restore CheckNamespace
{
    public static class EnumeratorExtensions
    {
        public static IEnumerable<T> ToIEnumerable<T>(this IEnumerator<T> enumerator)
        {
            while (enumerator.MoveNext())
                yield return enumerator.Current;

            yield break;
        }
    }
}

NHibernateExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;

// ReSharper disable CheckNamespace
namespace NHibernate
// ReSharper restore CheckNamespace
{
    public static class NHibernateExtensions
    {
        const int DefaultBatchSize = 100;

        public static void BatchInsertWithTransactions<T>(this IStatelessSession session, IEnumerable<T> items)
        {
            session.BatchInsertWithTransactions(items, DefaultBatchSize);
        }

        public static void BatchInsertWithTransactions<T>(this IStatelessSession session, IEnumerable<T> items, int batchSize)
        {
            if (session == null) throw new ArgumentNullException("session");
            if (items == null) throw new ArgumentNullException("items");
            if (batchSize < 1) 
                throw new ArgumentOutOfRangeException("batchSize", "Cannot have a batch size smaller than 1.");

            do
            {
                using (var transaction = session.BeginTransaction())
                {
                    foreach (var item in items.Take(batchSize))
                        session.Insert(item);

                    transaction.Commit();
                }
                items = items.Skip(batchSize);
            }
            while (items.Any());
        }
    }
}