Turbosquid has lots of free stuff too. And textures.com (formally CGTextures) also has tons of free stuff.

vstrakh has it right though. It is sometimes more challenge to find and make things fit your game than to just make it yourself. The reality is that art isn't as hard as it seems. Now, GOOD art is much more difficult, as in what dedicated artists do. But "acceptable" for an indie gamedev type art is much easier to do. I personally have gotten better at using 3d software to create my art, because it was easier for me to learn the technicalities of 3d space and Blender's GUI, and letting the renderer do the lighting and shading, than for me to learn anatomy, coloring, shading, lighting, etc... Other people are better at different methods, like pixel art, or using vectors...to each his own. But the point is that if the game's art is all the same style, and is done at an "acceptable" quality, though not necessarily great, it is OK. Also, programmer art is good enough to get the game going, and then if you find it takes off commercially, you may suddenly be able to pay for one of those dedicated artist gods to redo the graphics for you.

I would recommend looking at gametextures.com - there are pricing models attached (clearly explained on the site) and the textures are material textures in general (metal textures, wood etc) that I then tend to extract sections for when skinning models - so not ready made isometric object textures, but something easily adapted. From personal experience, where I am okay with the coding and modelling but rubbish with the texturing, the textures on offer has helped me turn programmer art into something will a professional feel - excellent texture and very good support (with even the option to request specific textures).