Below is an outline of the online advertising services and tools in the digital marketing tools index.

Click on the link below each section for a page with more detail.

Paid Search Engine Advertising

Google AdWords – advertising platform of the world’s most popular search engine and it’s search and publisher partners.
Bing Ads – advertising platform for Microsoft’s Bing, some Yahoo, and other distribution partners.
Swydo – PPC reporting, monitoring and workflow.
Optmyzr – AdWords reporting, data insights and One-Click OptimizationsTM.
Wordstream – PPC software, free graders, managed services and agency solutions.
NinjaCat – PPC and SEO reporting tool for agencies.

Paid Social Media Advertising

Facebook Ads – huge audience, large percentage of them are daily users.
Twitter Ads – news-y audience.
Pinterest Ads – some people can advertise now, some are put on a waitlist.
Instagram Ads – inspirational / aspirational.
LinkedIn Ads – B2B audience.
StumbleUpon Ads – uncommon “ad” format.

more detail: Social Media Advertising Tools

Online Ad Galleries

note – in order to reliably see advertisement galleries, switch off any ad blockers.
The Facebook Ads Gallery – large gallery ads with several filters, by AdEspresso.
Rich Media Gallery – large and detailed resource for rich media ads, by Google.
Banner Ad Design Gallery – browse banner examples, or other design elements.
Google Image Search – enter “Exactly” your ad dimensions, plus a keyword.

Forums & Hangouts

/r/PPC/ – largest PPC subreddit at Reddit.
#PPCchat – Twitter chat about PPC, every Tuesday at 12 PM EST. [archive]
Quora: PPC – the general PPC topic at this large Q&A site.
Quora: AdWords – the AdWords-specific topic at this large Q&A site.

Podcasts

The Art of Paid Traffic – weekly, covers ads for Facebook, YouTube, Twitter, Google AdWords, Instagram, LinkedIn, much more.
PPC Rockstars – sporadic, strictly PPC focus with host David Szetela.
SEM Synergy – weekly, blend of PPC, SEO and related topics.
Marketing Nirvana – archived, some episodes are still relevant.
PPC Playbook – archived, some episodes are still relevant.

Industry Blogs

Google Inside AdWords – official blog of Google AdWords.
Bing Ads – official blog of Microsoft’s Bing Ads.
Search Engine Land – SEM category of the industry news site.
Search Engine Watch – PPC category of the industry news site.
PPC Hero – popular blog focused exclusively on PPC.
Tenscores – long, though provoking posts on PPC.
Moz – PPC category of the popular blog. Infrequent, but in-depth.
Beyond The Paid – blog of Melissa Mackey, frequent contributor to #PPCchat.
Clix Marketing – agency blog about PPC, display and social advertising
The RKGBlog – agency blog about online marketing, with a good deal of PPC.
Certified Knowledge – includes posts by AdWords expert Brad Geddes.
iSpionage – blog of PPC/SEO competitor research tool vendor.
Acquisio – blog of search marketing platform vendor.
WordStream – blog of PPC analysis/optimization tool vendor.
Boost Blog – blog of ad creative tool vendor, features “win of the week” ad makeover.
CPC Strategy – retail advertising news, include paid search and comparison shopping.
Jon Loomer – in-depth information on Facebook advertising.

YouTube Channels

Google AdWords – keep up with AdWords changes with regular updates from the Googlers.
Koozai – whiteboard videos about PPC, SEO, branding, social networks and more.

Certifications

Google AdWords Certification – by Google, free, last for 12 months.
Bing Ads Accredited Professional – by Bing Ads, free, last for 12 months.

Courses & Education

Udemy – Google AdWords courses (various).
Market Motive – pay per click advertising certification course.
Online Marketing Institute – digital advertising courses.

Conferences

Hero Conf – major PPC events, one yearly in the US and the UK.
ADworld Experience – PPC event in Italy.
PPC Masters – PPC event in Germany.
Incite Programmatic Summit – event in Chicago, IL, USA.
Programmatic Media Summit – event in Phoenix, AZ, USA.
Programmatic Pioneers Summit – event in London, UK.
ad:tech – many media/technology events in the US, Europe, Australia and Asia.
Ad Age Digital Conference – event in New York City.

more detail: Digital Marketing Conference Calendar