paint, paint.net, gimp, photoshop

a good digi-cam

and if u want to create shader-textures, you will also need a normal-map generator

MS paint is not advised for making textures.

and if you're interested, you could try Filter Forge 2 (its a paid program, and an expensive one) to create textures out of available filters with any setting, resolution, color etc you want. most of its filters support more than just the diffuse map.

Then in-game, for standard textures, put in a cfg file in the folder "mysterious" :
texture 0 mysterious/folder ROT (X OFFSET) (Y OFFSET) SCALE

EDIT : Then in the map cfg file, put :
exec packages/mysterious/package.cfg

i once heared on quadropolis for this nice texture program:
http://www.mapzoneeditor.com/

try out yourself!

I like CGTextures, and I use the GIMP for editing.

thx for this great sites BlikjeBier !
I exactly found the textures i was looking for.

Creating:
Texture Forge - free thirty day trial- [ Removed ]
Editing:
Photoshop: if you have about 300 lose dollars hanging around
Gimp: Free open source

http://www.ehow.com/how_6167615_create-specular-maps.html
http://www.ehow.com/how_6167615_create-specular-maps.html
http://www.ehow.com/how_5122000_create-normal-map.html

Hope this Helps
Chasester

Edit by Windecker: Talking about bypassing application trial times, or anything related to unfair use is not permitted.

And in other news, I'm looking for texture artists--or even just people who've made the odd texture--who have made either one-off textures or texture packs and are interested in having them showcased.
If you've made textures, please send me an email at sheeettin@gmail.com or use Quadropolis' contact form. Thanks. :)