Most blogs have a resource/useful links page on their site and this can be a prime place to sell link placements to other webmasters.

I've seen this a lot in the travel niche where travel companies pay to have their link placed on the 'trusted partners' page of a travel blog.

Advantages: This takes barely any time at all to set up and you can sell multiple placements on the page to make a steady flow of extra income. I've seen some pages that have hundreds of links, so if you're selling the link for around $30-50 per month, you can end up making a good return.

Disadvantages: As this is another method that involves selling links on your website, it goes against Google's TOS, which as I've mentioned can land you in hot water.

As well as this, demand for static links that aren't wrapped within content have dramatically dropped over the past 18 months, so you may struggle to find advertising partners (unless that page has the potential to drive through a lot of traffic to the advertiser's website).