I will throw my support behind the Para2 as well... though you will likely pay a bit over your $100 limit. Legend tells of a time when you could get them for just under $100
... but they've been rare as hen's teeth lately so those out there have had been premium priced. That said, it looks like Spyderco is getting them out there again in time for Christmas (a few online retailers have them again).
If you want to stay in the Spyderco family the Manix2 seems to be a really great knife too. It's a good bit heavier than the Para2 (unless you get the lightweight version in the translucent blue... which I don't really care for) but it is less expensive too. It's significantly broader than the Para2 though and thus takes up a good bit of pocket real estate (which is what's really prevented me from getting one thus far).
Under $100 though leaves a wide range of very good options for EDC. Kershaw makes a ton of good value-priced stuff designed by RJ Martin (Chill, RJ I&II, etc) which I really like and for the money is tough to beat (around $20 give or take a few $). Spyderco's Value Line (Tenacious, etc) is good too, but after having owned a couple non-Value Spydercos (Para2s), their Value Line doesn't thrill me as much anymore because the higher priced ones are just sooo much higher quality IMO.
Another to look at is SOG... I have their Mini-Aegis and it's a great little knife. About $40 if memory serves, 2.0oz... lightening fast (and slick) speed assist, great deep carry clip (tip-up only though--which is my preference)... one of my small knife rotation mainstays since getting it.
The CRKT Heiho (or Hissatsu 2 as it was originally known) is another great little knife I have (and love). Around $40 and with a cool torsion bar assist and traditional Japanese tanto blade (and another deep carry tip-up clip).
Also, I don't think any sub $100 discussion about EDC knives would be complete without mentioning the Buck Vantage Pro series (the S30V ones). You can get these from about $50 (for the small) to about $80 (for the large). Great platform for the money IMO (and deep carry tip-up again!). Another one of my mainstays.
All that said... if you are a
bit flexible on the $100 spending cap... get a Para Military2! You won't be disappointed...amazing knife!!!!