Here goes:
For coding I'm using Visual Studio 2010. I made a dummy solution that contains my project files and all the SGDK files. Having all the files in a solution makes for searching easier. Other benefits include auto-completion of types. It doesn't always work in every case but often enough to be helpful.
To compile, I've set up an external tool in Visual Studio to call a batch file whenever I hit F6. That batch file calls SGDK compiler in the Goplanes code folder.
As for graphics, to modify the existing sprites and to create new ones, I'm using Graphics Gale (
http://www.humanbalance.net/gale/us/). It supports and exports to 16 color bitmaps, which is sweet. It's a pretty good tool. I've done all the sprite effects with it so far.
I'm using SGDK's genres support to import sprite bitmaps using the resource.rc file. I wish I didn't have the same extension as a Visual Studio resource file

Whenever I accidentally load it in Visual Studio, it tries to interpret it as Win32 resources (dialogs, text, etc.) and that fails. Not a big deal, though.
For building levels, I've used Mappy since the beginning because that's what seemed to be the tile editor most used around here. I took Kaneda's MDPPY's exporter plugin, added support to export C code, called it MDPPY++ and released it here
http://dl.dropbox.com/u/17303735/MDPPY% ... 01.1.0.zip. I kept working on the plugin but now it's pretty much geared for exporting to Goplanes. So it's not really a generic plugin anymore.
I export tilemap data to C arrays and structures. I'm not using genres's support for Mappy's format since it doesn't fit my usage.
Mappy was workable at first but I got tired of some of its limitations so I decided to look around for an alternative. At Chilly Willy's suggestion, I looked at Tiled.
http://www.mapeditor.org/.
Tiled is open source, and supports external exporters as DLL written in C++. Getting it compiled and running was incredibly smooth. It's written in QT Creator which I never used before but it was pretty straightforward to install and get running. Getting debugging to work took about a half hour to figure out but after that everything was fine.
It went so well I ended up writing two plugins for Goplanes for Tiled, a tilemap exporter and an object spawn point exporter. I thought moving to Tiled would be a big pain in the ass, but now I'm much more ahead now than I was with Mappy.
For emulation, I'm using a modified version Kaneda's Gens KMod. Orignal:
http://gendev.spritesmind.net/page-gensK.html. I first added Visual Studio 2010 support to it, that version found here:
http://dl.dropbox.com/u/17303735/gensKM ... io2010.zip.
I then added fixes to things I found annoying. I don't remember the entire list off hand, but I added things like:
- save the restore the position of the debug window
- toggled the debug window with a hotkey
- removed the 32k limitation of the debug window output. it's not perfect, but at least I don't have to manually clear the window whenever the text box is full, which happened often.
I should put up that version on my Dropbox so that people can get to it.
What else? I'm running on a Mac so I have a Windows XP install running in Virtual Box. The only problem that's been causing me is Virtual Box's iffy OpenGL/DirectX support. Some emulators don't work well since they can't instantiate a primary buffer. Getting Gens to work involved changing the display settings to 16-bit color.
That should be it!
If you have any questions, I'll do my best to answer them.