Other PPC Options

Advertising is key to popularizing your venture (website, product, app, etc.). I have used Google, Yahoo and Facebook advertising in the past. The response has been definite, but the lasting impact was poor. If you're not going to get a sustained bump, go for the cheapest effective advertising possible. Have you had experience with these advertising networks? I would love to hear your opinion. Which ones required a high deposit? Which ones provided good conversions?
Here's a list of pay-per-click (PPC) advertising venues:

7Search | Pay-Per-Click Search Engine Advertising Network - 2nd tier but Cheap search ads
Ad.ly - Celebrity Endorsements in Social Media - sponsored/celeb Tweets,Twitter Advertising
Adblade - Online Advertising and Monetization Services - self serve display ads, good traffic
adBrite Exchange - display/contextual ads
Select Country - Adconion Media Group - video/banner ads, media buys
http://www.addesk.advertising.com - display solutions on AOL inventory
AdBuyer.com provides the tools to help search marketers keep growing - media buying ad exchange
AdClickMedia Advertising Network - Pay Per Click Advertising, online text advertising, banner advertising, and Interstitial advertising. - self serve banners and contextual widgets.
AdEngage - Engaging Internet Advertising - banners/text, similar to adbrite, allow weekly buys
Adknowledge.com | The leading long tail marketplace - social media ads,cheap ads,High Volume - they require a deposit of $500.
AdMob | Promote Apps | Monetize Traffic | Measure Performance (Mobile)
Adperium Direct Ads - display banners, self serve, similar to adbrite
AdReady | Create an ad targeted to your customers - display ads/self serve banners on yahoo sites
AdRoll - Retargeting and Display Advertising - self serve banners
http://www.adsrow.com
AdSide: Beyond Standard Ads - self serve contextual inline text ads
http://www.adsonar.com - part of advertising.com(aol) -text ads on high traffic US sites like,cnn,cnbc,Huffington post,etc
Advertising.com - display/banners, media buys
Advertising | eZanga.com Hop on and go! - cheaper search and contextual
The Microsoft Media Network - microsoft banner display/media buys
http://www.bidplacesb.com/ - self serve banners, owned by AOL
BidVertiser - Pay Per Click Advertising On Sites Of Your Choice. - contextual and banner ads
Blog Ads - banners/text ads on high traffic blog network
BURST MEDIA - banners/display/media buys
BuzzCity - Mobile Internet Advertising (Mobile)
Online Advertising Marketplace | BuySellAds.com - self serve banners on a range of design blogs
Canoe Klix - text ads on the canoe.ca network
Casale Media - Home - self serve banners
Chitika - Online Advertising Network | Search Targeted Ads, Mobile Ads & Local Ads for websites, blogs, apps & mobile - search related contextual display ads
Clickbooth CPC Network for Advertisers or Affiliates - (Formerly Adtoll)-display/text ads
Online Contextual Advertising and Behavioral Marketing Services - contextual/banners
Home | Collective | The Audience Engine - media buys, banners/display
http://contextweb.com (formerly Adsdaq) -contextual ads/media buying exchange
CPMStar - The Online Network Devoted To Gamers - banners display targetted at gaming sites only
Welcome to CPX - banners/display, media buys
DSNR Media Group - Result Based Online and Mobile Advertising - display, media buys, unknown quantity/quality
Deck Trade (Mobile)
Elephant Traffic - ppv type ads on parked url's - cheap clicks
Etology - Advertising 2.0 - banners/text ads, cheap
Advertising | Facebook - self serve ads on Facebook (link removed)
FinditQuick.com - cheap text ads
Google AdWords - Large, expansive and expensive! (and their admin system is a little slow)
HUNT Mobile Ads (Mobile)
Marchex Pay-Per-Click Site-Specific - Contextual Pay Per Click Solutions for Advertisers and Publishers
InMobi | Global Mobile Ad Network (Mobile)
Targeted internet marketing - online advertising - online analytics - interclick - banners, high volume media buys
Self Service Advertising and Direct Sales Tool For Publishers | isocket (aka BuyAds)
Jumptap | The Leader In Targeted Mobile Advertising (Mobile)
Contextual In-Text Advertising and Related Information Solutions by Kontera - inline contextual text ads
AOL Advertising - retargeted ads at search traffic
World's Largest Professional Network | LinkedIn - Ads on Linkedin pages
Matomy Media - banner/display media buys
Media Traffic - CPV PPV Contextual Advertising - ppv ads - You need to prep and fax an application form. That put me off because it feels right out of 1997.
MediaWhiz | Home - banners/display, media buys
https://adcenter.microsoft.com - search and content text/contextual ads
Connect with targeted users on Adknowledge Miva | MIVA.com - cheap search ads
http://myads.com - self serve banners on myspace & a host of Fox network sites
Mobile Advertising, App Advertising and Analytics, Mobile Ad Exchange, Mobclix (Mobile)
Mobile Advertising with Mojiva's Mobile Ad Network (Mobile)
AOL Advertising - aol banner ad/media buy network
Free Online Dating at Plentyoffish.com™ - Social media self serve ads.
Dashboard Ad - premium banner ad networ
PubMatic - ad network
Pulse 360 - The Leader in Content Targeted Sponsored Links on the Web's Best Sites - ads on good high traffic inventory
www.quattrowireless.com (Mobile)
Réseau Sélect - Accueil - banner and offline targetted at quebec
Right Media - self serve banner exchange
http://rockyouads.com - social media display ads
Connect with targeted users on Adknowledge Miva | MIVA.com - search/contextual on parked pages. ****.
Home - Specific Media - banners/video display, media buys
Twitter Advertising : Sponsored Tweets - sponsored twitter posts
StumbleUpon.com: Discover the Best of the Web - Social media ads
Technorati Media | social media at scale - banners
Traffic Vance - good ppv ad network but you need to be referred to join
TRAFFIQ - self serve banners, media buys
trianads.com - failbook app ads, display
Tribal Fusion - media buy banner network
Undertone | The Singular Choice for Quality Display and Video Advertising - premium banners/display/media buys
Yahoo Marketing Solutions - search/content contextual ads
Hosted Audio/Video Chat Software by Userplane - social media advertising for media buyers
ValueClick Media | The Pure Performance Network - banners, display/media buys
Widget Bucks - self serve text/widget ads
ZestADZ - Mobile Ad Marketplace | Mobile Ads Network | Mobile Advertising and Publishing Platform (Mobile)