Although the physical marketplace still dwarfs the digital marketplace by a fair margin, the trend is definitely changing. With trillions of dollars of purchases now happening digitally and for digital goods - the industry offers great opportunities for many entrepreneurs. Here, we look at some of the top selling digital products and services. Some are old staples while others are just beginning to gain popularity - all of them, however, offer great opportunities.

Here are some of the top selling digital products:

E-books. Not only are E-books one of the top selling digital products, their sales are growing even faster with increasing penetration of devices like the Kindle. The rapid increase in interest for Indie or self published authors is leading the charge in this category.

Pictures and Illustrations. Photographs are another top selling digital commodity. Many online websites are selling hundreds of millions of photographs every year and the number is increasing rapidly. The key here is to stand out in the crowd and have a compelling story behind every picture.

Apps: In revenue terms, this is the biggest segment of the digital marketplace. There are billions of apps being downloaded every year and although the majority are free, there is still a huge market for paid apps.

Music. A rather tough niche to break into, but for the lucky few this multi-billion dollar online segment offers massive opportunities.

Online Courses. Everything from Do-It-Yourself videos to complete online educational courses are on offer by various sellers. It's a fast growing segment and the best part is that there is always an untapped niche of the market which can be tapped into.

Content creation. Websites and businesses are paying billions of dollars to writers to create content that is engaging and varied enough to satiate their users. Everything from informative blogs, optimized landing pages to search engine optimization etc. is being utilized to maximize web traffic.

Software and games. The majority of software and games are now sold online through various platforms. With fast internet being available to most users across the world, the online dissemination of games and software has become very rapid, thus boosting this segment.

Graphics and art. Think logos, icons, wallpapers, themes, banners and everything else that makes content pop. Graphics that stand out, and their creators, are always in high demand.

Websites. Creating and selling websites for the thousands of companies that are trying to get an online presence has been a good business for some time now. However, the trend does not seem to show any signs of slowing down and remains a top digital service.

Data. Business owners and entrepreneurs are convinced that the right data and an insightful analysis can help their business succeed. Building efficient databases and using the right tools to extract the relevant information to help businesses is a key service.

There are, of course, thousands of other digital products that are sold successfully online. The key is to offer something unique to the customer that binds them to you. While selling internationally, it is imperative to offer options that allow for payment flexibility and user experience customization. Platforms like Payzoff allow online merchants to offer to their customers the ability to pay using dozens of options from around the world - a key offering in a competitive marketplace.