What is the best historical stock market investment since 1985?

A cool question!

I measured this from 12/31/1984 to today. Amongst US companies trading today that were around back then, we have (I rounded the returns a bit):

#1 Amgen (AMGN) : 59,610%
#2 United Health (UNH) : 44,919%
#3 Franklin Resources (BEN): 44,147%

So Amgen, the Biotech, wins! On the longer list provided in the answer above from 1988, note Dell did not start trading until 1988 and NTY did poorly during 1984-88. and GAN did not start trading until 1986.

Hope this helps!

Some of the best include Enron and Adelphia.

Check out Wells Fargo stock...WFC.

Here are 18 that have +10,000% gains (with dividends reinvested) since 9/1/88, the beginning of data at http://www.fasttrack.net

1,UNH,UnitedHealth Group,46405.20%
2,NTY,NBTY,36749.60%
3,DELL,Dell,30161.93%
4,GAN,Gainsco,29377.01%
5,APCC,American Power Conversion/Disc,25734.23%
6,KSU,Kansas City Southern,22458.69%
7,QSII,Quality Systems,18075.70%
8,JKHY,Jack Henry & Associates,17787.13%
9,EMC,E M C Corp Mass,17383.55%
10,AB,AllianceBernstein Holding LP,14817.50%
11,SCHW,Charles Schwab,14673.99%
12,FNF,Fidelity National Financial/Disc,14495.93%
13,PLLL,Parallel Petroleum,14462.50%
14,SIE,Sierra Health Services,13234.04%
15,IGT,International Game Tech,12545.65%
16,BBY,Best Buy,11197.42%
17,WFT,Weatherford International,10825.43%
18,TEVA,Pharmaceutical Industries ADR,10084.55%