HGE

If you want to learn about the inner workings of isometric engines then look for articles by Geoff Howland and Jim Adams at at the following location
http://www.gamedev.net/reference/list.asp?categoryid=44

If want to avoid writing your own tile editor then check out the following
http://www.cornutopia.co.uk/
http://www.tilemap.co.uk/mappy.php

Also visit http://www.isometrix.org for info on isometric engines.

And post here your gamedev links that could be useful to others.

A good example of how to build 2d side scroller
http://www.2dgame-tutorial.com/

A 2d tile base engine tutorial... Code is Delphi but easy to follow
http://www.alistairkeys.co.uk/tiles1.shtml

A* tutorial
http://www.geocities.com/jheyesjones/astar.html

Amit's Game Programming: this guy has it all AI, pathfinding, design, scripting... and more
http://www-cs-students.stanford.edu/~amitp/gameprog.html

Good Reference Database from AngleCode
http://www.angelcode.com/refdb/

Pixelate is a webmag that got a lot of good stuff in it. (Some using the Allegro library, but could be useful anyway)

Not exactly Game programming, but still has some <very> useful information for stuff like String/Int Conversion, Reading Files, Namespaces, Coloring text in the console, loading pictures in the console, etc:

http://faq.cprogramming.com/

{Not that you have to worry about much of that in HGE :D }

Here're several good sites with some good tutorials:

http://www.gotoandplay.it/_articles/

http://ydjapan.blogspot.com/ (look for the excellent "Beat-Em-Up Fighting" tutorial series on the sidebar)

They're for flash but one could translate it for HGE. The "DEMONWITHIN" demo is pretty interesting. I've always wanted to put street fighter characters into a side scroller. :)