I have a circa 2006 Ruger mini 14 in a black standard synthetic stock. Tons of fun. Ive always liked that Garand style action. Yes, I have a Garand as well.
I've purchased from Gunbroker BC (before Chris), with good results. A good seller will include tons of photos, including a look at the barrel rifling (well lit). Also look for wear on the feed ramp/throat area, as well as the front muzzle of the gun. Email the seller and ask for more photos (specific ones) if the posted ones are inadequate or out of focus (common).
Here is a little info I had wriiten down regarding the different series mini's:
180 Series Link
Produced from 1974-1977.
Brass ejects upwards.
Shipped from factory with wood handguard installed.
Original Mini-14, no longer supported by Ruger (i.e., no 180-specific parts available)
181 - 186 Series Link
Produced from 1978-1999.
"Standard" Mini-14
No factory scope mounts, single blade front sight, low round rear peep sight.
Brass ejects upwards.
Still supported by Ruger factory parts.
196 - 197 Series Link
Produced from 2000-2004.
Same as 181-186 Series.
187 - 188 Series Link
Produced from 1982-1995.
Mini-14 Ranch Rifle
Factory Scope Mounts, flip-up rear sight, single blade front sight.
Brass ejects to side to avoid contact with scope.
Still supported by Ruger factory parts.
195 - 197 Series Link
Produced from 1996-2004.
Mini-14 Ranch Rifle.
Same as 187-188 Series.
580 - 581 Series Link
Produced from 2005-Present.
Mini-14 Ranch Rifle.
Winged Rear Peep Sight, Winged (3-blade) Front Sight.
Integrated Scope Mounts.
At some point in the 580 Series, Ruger introduced the "heavier," flanged/tapered barrel which improved accuracy and decreased heat sensitivity (stringing).