Perhaps you're not interested in a glass cockpit, and you want more realism than pictures can provide. Populating your instrument panel with simulated instruments will, IMHO, present you with a definite step up in realism.
One very real option is buy simulated instruments.
The past few years have seen the formation of small flight simulation firms that have taken official notice of the flight sim hobby community. Sea Gull Simulation Systems & Parts, SimKits (one of The Real Cockpit companies) and Sim Instruments all manufacture "steam gauge" style simulated instruments and make them available to hobbyists. A very nice feature of these companies is that they also offer interfaces to personal computers and recreational flight sim software.
There are a number of other sources of simulated instruments, of course. Firms such as Aircraft Instruments, Inc. and Control Tech, for example, have been around for years making instruments for the commercial and military simulation markets. They make high quality gear, and because they have been in existence longer, may offer more variety. However, because of their particular market focus, it's unlikely they will offer interfaces suitable for recreational flight sim. So, while you may find unique simulated instruments, you will quite likely have to interface them to your sim yourself.
Interfacing should not be considered a show stopper, though you may find it an annoying distraction if you're more into flying than building. An interface can be built from scratch. Alternatively there are commercial interfaces such as the EPIC system which may be suitable, depending upon the instrument's interface requirements.
Another option: Conversion
Another option, at least for some of the single pointer type instruments, is to use an after market marine or automotive tachometer. Prices and styles vary widely. Some styles present a "high tech aircraft" look and may appeal to you. (Check on-line discount stores like J. C. Whitney.) You will need to modify the faceplate to suitable aircraft markings, as well as handle the interfacing issue. These units typically are designed to be wired to an engine's ignition system, so require a variable frequency pulse source to drive them. (A excellent application of a $3 micro controller and a bit of firmware.)