Most important gauges (to me) are (in my order of preference):
1) tie: Oil pressure / oil temperature: With the turbo, you NEED to know when the oil is warm and "flowy" enough to get into the boost. Water temp won't tell you that, as the water warms faster than the oil.
2) Boost: Because it's cool, the needle moves a lot, and it helps to know to stay OUT of the boost until she's warmed up (see "1" above...)
3) Volts: Because it's good to know. Ordinarily this would be the first to tell you a "fan" belt is shot, but (especially with a powerful stereo) it's a good piece of info to have.
Now I have to re-read the posts above to find the ones that best match the interior colors - designer or not, I'm buying them once, probably taking a bunch of time (and/or money) to install them, looking at them often, and I want to be reminded of what they're telling me rather than "well, they're OK, I got 'em cheap"!