I might be falling into a pattern...

For now I just want to collect all the sources in one place. The list is somewhat sorted but hopefully I'll go over this list again and summarize all/most of them and maybe do some more sorting.

A quick heads up: There are a lot of duplicate links but I wanted to document for myself how/where I found the projects.

Hakko 907:

• I already mentioned this one which was featured on the blog - I really like the option of driving two irons and the author makes a good point for the analog dial. He also proposes a mod for better heat conduction between the heating element and the tip.
• Right now I'm thinking whatever I'll end up building is going to be very close to #Hakko 907 based Soldering Station because it's very straight forward.
  • derivative: https://hackermagnet.com/portfolio/soldering-station/
• http://elco.crsndoo.com/wordpress/2012/01/soldering-iron-driver-gen3-rev1-4/, via http://dangerousprototypes.com/2011/10/25/hakki-907-and-compatible-soldering/
• #Soldering Iron Controller - (light on info) / more info: http://www.zl2pd.com/SolderingStation.html - (analog & digital control), via http://hackaday.com/2015/09/02/a-tale-of-three-soldering-iron-controllers/
• #Mobile temperature controlled soldering iron - links for components

Hakko T12

• http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=5264&start=180#p58264 / http://dangerousprototypes.com/2014/07/01/hakko-t12-soldering-controller/
• #70W Soldering Iron Controller / http://smdprutser.nl/project/70w-soldering-iron-controller/
• @Stefan Wagner's #Soldering Station and #TinySolder 

Weller RT:

• http://www.martin-kumm.de/wiki/doku.php?id=Projects:SMD_Solderstation, via http://dangerousprototypes.com/2014/05/29/smd-soldering-station-for-weller-soldering-tips/
• https://debugginglab.wordpress.com/2014/10/30/soldering-station/ / https://github.com/ConnyCola/SolderingStation - based on above, very nicely thought out (has standby feature), PCBs on DirtyPCBs
  • derivative: https://github.com/PostTenebrasLab/SolderingStation
• http://hackaday.com/2015/05/11/hacking-amazing-soldering-features-into-the-already-great-weller-wmrp/
• #Soldering pen by @HP (@banjohat) - also based on the one by [Martin Kumm] linked above, very cool idea of integrating all the controls in the handle, made me think about applying this concept to the 907 iron/handle
• See also the projects in @Teslafly's list rt usb_c soldering iron

Weller WSP80:

• http://www.eosystems.ro/index.php/projects/esol - uses MCU's internal PGA
• #Yet another DIY soldering station by @SUF - expected to have 3 (!) soldering irons and a bunch of other useful features, especially like the ideas to reduce energy consumption

Modded mains soldering iron:

• https://pcbsmoke.wordpress.com/2015/10/03/diy-110v-temperature-controlled-soldering-station/, via http://dangerousprototypes.com/2015/10/05/diy-110v-temperature-controlled-soldering-station/
• https://pcbsmoke.wordpress.com/2015/08/03/soldering-iron-temperature-controller-version-2/
• https://pcbsmoke.wordpress.com/2015/07/12/diy-digital-soldering-station/, via http://dangerousprototypes.com/2015/07/14/diy-digital-soldering-station/
• https://pcbsmoke.wordpress.com/2015/06/04/soldering-iron-pulse-timer-temperature-control/, via http://dangerousprototypes.com/2015/06/05/soldering-iron-pulse-timer-for-temperature-control/
• https://pcbsmoke.wordpress.com/2015/04/21/soldering-iron-pid-temperature-controller/, via http://dangerousprototypes.com/2015/04/27/soldering-iron-pid-temperature-controller/
• #Entry Level Electronics -- Improve your Iron

Misc:

• http://poormanelectronics.blogspot.ro/p/pm-soldering-station.html
• http://dangerousprototypes.com/2016/02/03/unisolder-5-2/ - universal controller
• @monsterome's list SOLDERING STATION DIY

While I focused on soldering stations here, you might also want to check out the official soldering-tools list if you haven't already.

Edit 2016-03-28: Added #Soldering pen

Edit 2016-03-28 #2: Added http://www.eosystems.ro/index.php/projects/esol

Edit 2016-05-07: Added #Yet another DIY soldering station

Edit 2022-09-05: Added links to curated lists and some more projects