Like everybody else, I could throw out my favorites, but you kinda need to know your target.
If they don't care for sipping whiskey and are just going to mix it in Coke, basic Jim Beam, Evan Williams or Wild Turkey is fine. WT101 is a fine mixer or sipper.
Maybe a nice Rye for someone who likes bourbon cocktails. Rittenhouse (Heaven Hill), Sazerac are solid on the low end. Russell's Reserve, Wild Turkey 101 Rye, Willett are all a notch above. Pikesville (Heaven Hill) at about $50 is the best Rye I've ever tasted. Whistlepig is ridiculously expensive for what it is to me.
For somebody who knows whiskey and can handle some that are much higher proof these are my can't miss bottles: Eagle Rare (it's effectively smoother, better, older Buffalo Trace), Wild Turkey Rare Breed (WT is one of the world's great whiskeys, most don't realize it), Henry McKenna 10 year BIB (Bruce said it best above, make sure its 10 year, bottled in bond single barrel), Knob Creek 120 Single Barrel (Beam's best under $50 to me), Maker's Mark Cask Strength (I don't love Maker's, but wouldn't pass up a sip of this), Old Forester 1920 (best of Brown Forman under $60 or so to me) Blanton's (consistent in a beautiful bottle, important in bourbon history).
Also, Willett Pot Still is in stores now. Average bourbon to me, but as a gift the bottle is cool as hell.
Scotch whisky is a whole nuther thing to me. Need to know for sure that your receiver likes Scotch first and foremost.