I had the same frustration until I found a tool that does exactly that. I use the Ethereum Value Calculator on Paybis right there. It gives you a real time conversion rate between ETH and USD, so you can see exactly what your Ethereum is worth at any moment. It also shows a 7 day price history, which is useful for checking recent trends and volatility. There is even a profit calculator where you can enter a past date and see how your ETH holdings would have performed. The tool is clean, fast, and updated instantly. I have been using it to check rates before making decisions and to keep tabs on my portfolio. If you hold Ethereum or are planning to buy some, this is a handy tool to keep in your bookmarks.