The original iPad mini doesn't have retina display. There are minimal differences between both devices (mini and mini with retina): retina is slightly thicker and heavier. It has MIMO (original mini doesn't) and 3 x video zoom.
If you purchased the mini before November, it certainly is without retina. They look equal, so there's no way to find out which one you have by just looking at them, if they're not next to each other, or the screen is locked.
The retina mini has two microphone holes, one on the top (same as the 1st gen mini) and one on the back near the top of the device (close to the one on the top). This is the only way to be sure without actually using the device. Of course, the color schemes are different two.
The recently-released iPad Mini with Retina Display will have one of two model numbers printed on the back of each unit in very fine print : A1489 or A1490.
Yeah if you do decide to get a iPad mini I would definitely recommend it with the Retina Display and a lot of people here would agree. Visually it is a whole lot better and you wouldn't be disappointed.
All iPad mini's do not have Retina Display so if you decide to purchase one you should ask before you purchase to make sure that you get what you want. Go with Buck Falcon advise on the model numbers.