Its no substitute for the real thing, but I recommend RANT 2000. Its used by a lot of the training schools and helped me no end with getting my IMC, especially if used to practice exercises just before flying.
Its not supposed to simulate real flying, but it allows you to concentrate on getting to grips with interpreting the instruments.
Details available at
http://www.oddsoft.co.uk/news.html or at the shop mentioned above.