Decide.com: the Buyer's Decision Engine
It's particularly useful now. That old maxim used to apply mostly to PCs and larger electronics. Now it applies to so many things, including smartphones and tablets, that it can be a confusing mess in your mind.
Ah, but both of those aren't covered yet (smartphones and tablets). What are covered are TVs, laptops, and cameras. Specify the product name within those categories, and Decide.com will give you a "Wait for a New Model," "Buy," or "Wait for a Price Drop" recommendation.
For example, enter MacBook Air, and you're given a "Wait for a New Model" suggestion (it's known that Apple is planning a refresh with Sandy Bridge and Thunderbolt I/O soon). It even links to sources that talk about the refresh.
Type in Dell XPS 15z and you'll get a "Buy" recommendation which adds "Prices not likely to drop." That's another part of Decide.com's data mining. Not only does the site mine the Web for rumors, it also has predictive pricing algorithms to help users find the right time to buy in terms of possible price drops.
In addition to the query, a user can set filters. For a laptop, the filters include screen size, processor, RAM, price or brand. If a user decides to buy, he's connected to a partner store (like Newegg, for example).
Anything that reduces buyer's remorse, or even non-buyer's remorse (not buying at the right time) is something we're all for. Now, if they could just create a program to determine the right time to trade a stock ...