While using classified ad sites for building backlinks certainly is not one of my preferred methods, it does work.
Top Classified Ad Sites:
adlandpro.com
backpage.com
craigslist.org
gumtree.com
hoobly.com
kijiji.com
theadnet.com
usfreeads.com
More Classified Ad Sites:
Ablewise.com
Adoos.us
Adpost.com
Adquest3d.com
Adtrader.co.uk
Adtrader.com
Albertarose.com
Buysell.com
Caklassifieds.com
Chooseyouritem.com
Citynews.com
Classifiedads.com
Classified-ads-4free.com
Classifiedextra.ca
Classifieds.co.uk
Classifieds.myspace.com
Classifieds.yahoo.com
Classifiedscrossing.com
Classifiedsforfree.com
Domesticsale.com
E-classifieds.net
Economist.com/classifieds
Epage.com
Ezilon.com
Freeads.co.uk
Free-advertising-blog.com
Freeadvertisingboard.com
Freeadvertisingexchange.com
Freeadvertisingforum.com
Freeadvertisingzone.com
Friday-ad.co.uk
Google.com/base
Iclads.com
Inetgiant.com
Isell.com
Itsmymarket.com
La.kaango.com
Livedeal.com
Loot.com
Marketplace.sfgate.com
Olx.com
Oodle.com
Postonce.com
Postyouradforfree.com
Recycler.com
Salespider.com
Seethisitem.com
Sell.com
Selloutads.com
Subblurbs.com
Sunrad.com
Tauque.com
Theflyer.com
Thefreeadforum.com
Traderonline.com
Tytia.co.uk
Uk.freeads.net
Uscity.net
Usnetads.com
Vflyer.com
Villaricaclassifieds.com
Vivastreet.co.uk
Webpagepublicity.com
Worldslist.com
(1) The jury is still out about whether there is added value in getting backlinks from sites in your niche (not talking about getting pass-through traffic, just the backlink value). Many many people feel this is way overrated, me being one of them.
(2) With respect to "do follow", it certainly has a value by google, but really no effect as to yahoo, etc.
(3) You briefly mentioned this sort of thing in the "hitch a ride" section, but IMHO the best and easiest way to get great quality backlinks is from putting links in your profile and forum and web 2.0 properties, where the underlying domain has a high PR. Many of us have had phenomenal success with this linkjuice.
(4) Not everyone agrees as to how much of an issue it is to get tons of backlinks quickly. Many believe that the whole Google sandbox thing is way overrated. If we are talking thousands and thousands to a new domain, then OK. but I don't think throwing a hundred of backlinks at a EZA article a day is going to do anything but help you get to the top of google.