Spam Links You Want to Avoid
Two things to keep in mind that can warrant spammy behavior when building links:
Type of Links – where you’re building links from.
Anchor Text Ratio – Good to keep ~80–90% branded/natural (i.e. domain.com, Your Brand/Business name, and then sprinkle in some exact/partial match anchors from authoritative sites surrounded with good content. Can get penalized if you try to link to your site with to many of your keywords.
Type of Links
It varies among industry, and where your pointing the links to. For example you can be much more aggressive sending spammy links to YouTube videos and still see sustainable rankings from it.
Off the top of my head these are some popular spammy links to avoid:
Blog Comments: I know a lot of SEO’s who use blog comments to rank sites. This is considered spammy, but some still get away with it depending on the vertical. I personally would use this vary sparingly and in the right context (commenting on a industry related blog, with valuable context justifying the link) but there are services that can automate it and as a result people who abuse it.
SAPE links are also used to be very popular way to link and still are in some verticals. But sooner or later you will get penalized if pointing these to you money site.
PBNs: Poorly set up private blog network links can get you penalized. These come in the form of link rentals, or links that lack content/context/semantic relevancy
This article on Moz  deems a lot of links “spam” that I’d disagree with. Moz is known for being incredibly “white hat” and are known to be teacher’s pets for Google and I often read misinformation from them compared to what I’ve seen work in the SERPs. Notably:
Press Release links – these work really well if your Press Release is well written and your anchors aren’t abusive, and you use a good service.
Directories: Directories and citation cites are a great way to build your branded/natural link ratio, especially for local businesses. Directories that are highly relevant to your industry are great links. i.e. A personal injury directory for California businesses if you’re a personal injury lawyer in California.
Web 2.0s – If you invest in quality content, and take the time to build a network, these can be really powerful. You can use these to link to your other social properties, Google + page, embed your YouTube videos…etc, which all help build topical relevancy around your site.
Forum Links – When used properly these are great links to demonstrate topical relevancy o your site.