There are several online movie download services that have established themselves as real players in the instant gratification film niche. The latest to join the fray is Apple with its iTunes Movie Store. You can download a film to your Mac, your PC or your iPod - although watching a feature link film on that three inch screen could leave you babbling into your popcorn box.

Apple is joining a number of existing online services. The largest among them include Guba, Movielink, CinemaNow and - who else? - Amazon's Unbox. With the exception of the Apple site, you're going to need a PC and in most cases, use the Microsoft Explorer browser to download your films. It's not just films that are available - many of the services have a TV library as well.

There are a number of variations among the sites - size of library, presence (or absence) of first run films, and variations in the licensing agreements. Without exception, your download will include digital rights management (DRM) technology which controls your use of the downloaded file.

The Apple store recorded one million sales in its first month of operation, seizing on its position in the media download market to get off to a running start. They feature Disney products, but these days Disney has a number of film genres put out under various labels. Their recent releases cost from $12.99 to $14.99 to download.

Amazon has deals with 20th Century Fox, Fox Searchlight, Lionsgate, Paramount, Sony, Universal, and Warner Bros. That's an excellent collection of partners, and their film lineup reflects it. You can download The DaVinci Code for just under fifteen bucks, and a show from TV's CSI for $1.99. They have been heavily criticized for incorporating some extremely intrusive software into their download process.

Movie Link is a partnership of several major movie studios, another example of content developers trying, successfully and economically or not, to create a distribution network. Their library is probably the best on the block, as the partner roster includes MGM, Paramount, Sony, Universal, Warner Brothers, Disney, Sundance Channel, BBC, and National Geographic. If you're searching for an obscure gem, Movie Link has the largest catalogue online. Their new releases are usually $19.99 and their better catalogue choices $9.99.

CinemaNow is the only service to have managed a film release simultaneously with the DVD release, which they accomplished with "Too Fast Too Furious." They also will provide the ability - for a price - to burn selected downloads to a DVD. Their licensed partners include Disney, Fox, Lionsgate, NBC Universal, Sony, and Warner Bros. Their prices for new releases range from $14.99 to $19.99 and their catalogue charge is $9.99.

Guba is the bargain download shop, with a library built on deals with Warner and Sony. They began originally as a Usenet service provider, and feature a Usenet uploads in their onsite search. Their prices top out at $9.99.

While Netflix has been talking about getting into the download business for two years, their service remains in the planning stage. They're going to be challenged when they make the transition from DVD to computer file, as many of the major movie houses have tied up their download rights in services that are their own creations, such as Movie Link or services in which they are partners.

The computer-driven movie-on-demand service is on the scene, and many think it will be the format of choice in a few years. A top end PC is capable of being a highly functional entertainment center, and the convenience of true on-demand films is going to overshadow even the most sophisticated cable TV on-demand services, as compression technology improves and download times drop.