In addition to my advice on drawing tilesets with Photoshop, I decided to do the same for vector graphics tilesets with Inkscape.
In the last months, I started to mainly use vector graphics for my game art. In case you don’t know, vector graphics and its standard format SVG are a way of representing graphics by storing mathematical descriptions (like position, size, color etc.) of geometrical objects. Besides common shapes you can also create paths and complex objects with an arbitrary number of edges and curves. By combining the different techniques it’s possible to model almost any object you can imagine.