Probably more than I'm aware of. Here's a list:
As usual, it depends. I started with Yashica because I lend my fathers camera and I didn't want to spend a whole lot on new equipment. Actually, I did spend a whole lot on a Nikon camera a year ago, but I found that autofocus didn't really work with me and that I couldn't afford the Nikon glass I wanted anyway. So I sold that and bought a lot of Yashica stuff for the money.
The great thing about Yashica is that it is completely underrated. The market is so small and demand is so low, that prices are way below what you pay for other brands, with comparable quality. Most people are quite positive about the quality Yashica delivers (both mechanical and optical).
The bad thing about Yashica is that the market is so small and supply is so low, that it can be quite hard to find something you need. More often than not, you are stuck with the option of forgoing a particular accessory or buying something with Contax on it, which is a quite expensive brand.
Mentioning Contax, that's the second great thing. The upgrade path is unique. You start with a Yashica body and Yashica glass, then upgrade to Carl Zeiss T* lenses, and finally upgrade to Contax bodies. In the meantime, you have your old Yashica stuff as a backup system, everything is completely interchangable.
Yashica has been around since 1957, and some old camera's, especially the twin-reflex camera's for the medium format, are still quite popular. In the seventies, Yashica licensed the Contax brand from Carl Zeiss and started producing high-end camera bodies under that brand.
Since the early eighties, Yashica is a part of Kyocera, and fills in the low half of the photo market for this corporation; Contax fills in the upper half. Contax bodies are made probably by the Yashica production facilities, Contax lenses are made by Carl Zeiss. For a nice history of Carl Zeiss and the Contax brand see History Of Contax/Carl Zeiss.
Yashica has been making 35mm cameras for a long time; the current line started with the introduction in the 70's of the Yashica/Contax mount (which we'll call the Y/C mount from now on) that is still in use. Before switching to the Y/C bayonet mount, Yashica made a fairly extensive line of screw-mount SLRs (TL Electro) with a full complement of Yashinon interchangeable lenses. The screw-mounts were preceded by the Yashica Pentamatic, which came out in the very early 60's and was the first SLR by Yashica. It had a bayonet mount and was offered with an Auto Yashinon 55/1.8 lens, plus 35mm, 100mm and tele lenses.
Furthermore, from early 60's and untill mid-80's Yashica designed and manufactured an extensive and highly successful line of 35mm full-frame (and half-frame?) rangefinders.
Contax is, from a marketing point of view, an entirely different brand. Manufacturing quality is better, too. However, rumours are that lots of engineering is in fact shared between Contax and Yashica, and lots of people combine the best value from both brands. I have a page on Contax equipment as well, at http://www.cdegroot.com/photo/contax.