After Google declared that sites selling text links without a label NOFOLLOW will be punished, this monetization method became less popular.
Many website owners are still using text links on their sites money, although some use NOFOLLOW tag, and some do not.
The advantage of this method is that it is not interference. You can sell text links directly from your website or use specialized networks like Text-Link-Ads and Text-Link-Brokers to automate the process.
Text links markets and networks:
* DigitalPoint Link Sales Forum
* Text-Link-Ads
* Text-Link-Brokers
* TNX
* LinkWorth