Hard to say. Commander Keen? Wolfenstein? Kings Quest? Star Control? So many good memories.
My allowance = spend $10 at the mall arcade, hit some shareware, buy some DOS game that I had to write my own batch file for, add in mouse support and hopefully get it to recognize my off brand sound card.
Quake. Oh and did I say Quake?
Secret Of Mana
Quake does rank up at the top of my favorite game soundtracks ... Trent Reznor was the perfect fit for that title ... http://www.youtube.com/watch?v=xgyjCCMbWlY&list=PL90ACFEE5615B8EB6
I don't lol, as kid in the 90s that was the only way I got games for the PC. I wasn't til like 2 or 3 years of playing the shareware version of Duke Nukem 3d and Warcraft 2. I got the full versions and was blown away.
Since then i had a sour taste in my mouth when it comes to shareware games.
Reading these replies reminded me of the demo discs that used to come in magazines. I had stacks of those discs, played the first level of so many games. I must have beat MDK's first zone 100 times.