When it comes to folders, Kershaw has some great US made models for less than $100. Blur, Leek, Knockout (my favourite) jut to name a few. The Launch series is also under 100 bucks.
Spyderco offers some of their best EDC model for less than $100, too. Endura (even the FFG ZDP189 variant is around 100 dollars), Delica, some of the Manix 2's, Dragonfly, Salt series knives, etc.
Benchmade has fewer options in that price range but the Griptilian and 530 are excellent knives.
Victorinox deserves a mention, too.
Last but not least, Cold Steel has a ton of folders for around that price. Recon 1, Voyager, Broken Skull, Code 4, Lucky, Rajah III, Tuff Lite, American Lawman, etc. Probably the toughest folders you can get for the price.
If you're looking for a fixed blade then Cold Steel, Mora of Sweden, Ka-Bar (I'm rather fond of their Becker line), Condor, Buck, Ontario, SOG all make decent tools within that budget.
It's hard to choose THE best one. A lot of it comes down to personal preference.