These are some VB6 IDE addins I have created or found useful.

CodeDB - mine 
   small util that has a code database and some other tools.

LinkTool - Jim White
   extended version of Jim Whites LinkTool to create 
   std dlls and link in C Obj files

MemoryWindow - mine 
   VC like memory window for VB6
   https://www.youtube.com/watch?v=MA210lrPxTQ

MouseWHeelFix - MicroSoft 
   adds mouse wheel scrolling support to IDE. (unmodified)

FastBuild - mine 
   streamlines vb6 build process
   https://www.youtube.com/watch?v=bLfvaYNIhzk

Tabs - CodeHelp 1.2.2  Author: Luthfi M
   nice lightweight and stable addin which adds
   tabs to the vb6 IDE. (unmodified)

CodeView - Patrick de Groot

  Addin for Visual Basic 6 that displays all procedures/functions
  variables/properties/constants of the currently selected 
  form/module/class/control. This way you have a better overview of 
  your code. It is a very usefull companion for the project explorer.

  Note filter supports subtractive filters too like "-mouse click" would hide 
  anything with either of those strings in its name..minus must be first character

IndenterVB6.exe - Office Automation Ltd - V3.5 - 2.10.2005
  The Smart Indenter is a utility to tidy up VBA code by rebuilding the indentation of each line.
  http://www.oaltd.co.uk/Indenter/Default.htm

SideBySideActX - 3 different open source tools and a couple articles for generating
  manifests so you can use your COM dependancies registration free. XPSP2 and up
  (how in the world did I never know about this until now!)

API_Add-In  - CVMichael ((Michael Ciurescu) - 2.3.2004 - replacement API viewer w/mods (soon to be)

hex_tooltip - C dll to inject into VB6 IDE - when debugger is running mouse over numeric values will show
   normal value display plus its hex representation. Loader will be added to one of the above sometime soon.