http://luizmonteiro.com/Learning_HSI_Sim.aspx
Some may already be aware of this one - It's a navigational training sim, and it's really well done. It has been around for years (the look of it betrays it's age), but it is still on the EAA's recommendation list. It allows you to understand and practice just about any IFR or instrument procedure without having to worry about piloting the aircraft (except on a very basic level). It's a bit daunting when you first see it, but with an hour or two of reading the well done manual (it's hard to find) - look on the purchase page) you will understand how it works. It can be used with analog gauges or a glass panel. It was originally Flash-based, and was offered for PC and mobile devices. With the demise of Flash. it is now only offered for the PC. It IS payware, and you may balk at the price, but as far as I am aware there is really nothing else like it out there, and is money well-spent. You can spend hours studying books, but there is nothing like seeing all this stuff in motion to really understand it. It can be downloaded and tried for ten days for free. Highly recommended!