1. YouTube

Google's acquisition of YouTube in 2006 for $1.6 billion proved to be one of its best investment bets. It is the second most visited website in the world today (as per Alexa Internet), which makes it one of the Google's best source of revenue from online advertisements.

As of February 2017, YouTube has over 400 hours of content uploaded every minute, while one billion hours of content is watched every day. Analysts predict a revenue of $15 billion from YouTube advertisements in 2018 (verdict.co.uk).

2. WhatsApp

When the founders started WhatsApp, they did not expect it to get so popular so soon. It had 450 million users around the world at the time when Facebook acquired it for $22 billion.

WhatsApp today has 1.5 billion users, and has added many additional features than what it used to be. With the amount of expansion in userbase, Facebook's investment paid off.

3. Pixar

Steve Jobs-led Pixar was changing the way animated movies were made in the early 2000s. It had made hit movies like "Finding Nemo" and "Toy Story" before Disney bought it for $7.4 billion in 2006. Pixar since then has produced various high-revenue animated movies.

4. Marvel

It is another Disney acquisition for $4 billion in 2009. Marvel before being acquired was a humble comic book and superhero franchise with famous characters like Mickey Mouse and Donald Duck. Since 2009, it has made over $20 billion worldwide in revenue just from movies alone, excluding merchandise sale.

5. LinkedIn

When Microsoft bought LinkedIn for $27 billion in 2016, it seemed like an overpaid investment. The subsidiary contributed $1.3 billion in revenue in its second quarter of acquisition with the help of 530 million userbase and online education platform Lynda.com.