In my opinion NovaSkin is better for mobs.

I don't know of any sites, but your best bet would be to download some kind of art program. Instead of searching for Minecraft texture makers, you should search for pixel art editors. Actually, any general-use art program will do, but one made for pixel art would be best. Basically all you're doing is editing plain old PNG files. The most important features you'll want are wrapping/tiling, which allows you to easily make seamless textures, and a high level of zoom so you can edit each individual pixel.

I personally like to use Krita (although it has a lot of extra features that might make it confusing for newcomers). There are many other similar art programs, but after some research, I found that not many of them have a tiling feature. If for some reason you don't want to install things on your computer, there is a free app (only for Android, however) called Pixly that is simple and very good for pixel art and Minecraft textures.

Why do you need a website for that?