Specifically protein bars, or energy bars? If the latter my favorite is the Cliff Bar. I also love the Nature Valley granola bars, they provide a good amount of energy, and taste pretty damn good.
For Protein, I like Clif Builder's Bar. For a time EAS had a bar (Phosphagain, iirc) that tasted great, but that was years ago, and I gave it up when I started running. For Energy, I like Clif - almost any flavor will do. Also Odwalla Cranberry C Monster is good for a change of pace. Their Chocolate/Peanut is great as well.
My two favorite protein bars are Powerbar ProteinPlus Chocolate Peanut Butter, and Pure Protein Strawberry Shortcake. Of course, the purists will tell you that protein bars are nothing but glorified candy bars and that to get a really good healthy protein bar without all of the added sugar and other bad stuff you should make your own: Protein Bar Recipies
Clif Bars are great. For just a snack I like Lara Bars. It's raw (uncooked, unprocessed) ingredients and I haven't met a flavor I didn't like. Angelo
Clif Bars are good... Clif Nectar Bars are divine. How could something like five ingredients taste so good?
Most protein bars are full of crap ingredients but marketed to appear 'healthy'. The only two I know of that are somewhat healthy: http://www.luckyvitamin.com/769745600110.html http://prolithic.com/hpages/efoods/elev8me.html
Detour bars are the best tasting bars I've had. These days I've just been mixing unflavored whey isolate into OJ.
I'm a big chocolate fan, so my two favorites are Met-Rx Protein Plus Chocolate Chocolate Chunk and Chocolate Fudge Deluxe. 320 calories, 34g protein. Most of the so-called protein bars have very little protein (i.e. less than 10 grams).
Tiger. much better tasting than Clif or Power but also probably not as nutritious since it tastes so good. it'd be great for an endurance activity where you're going to be losing a lot of calories a day like hiking or backpacking. probably too heavy for runners doing marathons though. there's always Ultralight Joe's Moose Goo: http://www.ultralightbackpacker.com/....html#MooseGoo -Jeff