The value of your internet assets is known, buyer can easily multiply the monthly revenue in 12 and offer you the price for the site/ blog/ forum etc. But the real value added, when the site is a real business, means: customers, sales, product or services and reputation. These are the details to present when you are looking to sell Good luck
interesting.. how to value the intangible is always the hardest part.. are you providing buying/selling/listing service? I know quite a few here are trying to sell their websites.