Blue Powerade is delicious. Gatorade tastes pretty good and you can get it in the less expensive powder form, but it has lots of sodium. Cytomax has more potassium, but it tastes soapy if you drink it alone. So I mix about 2 parts Gatorade to one part Cytomax. For very long rides, I might add some complete whey protein powder (vanilla flavor). Accelerade has protein already mixed in, but I just don't like the way it tastes and it doesn't seem to dissolve very well.

Gels: chocolate Power Gel. I really dislike the Clif gels -- too sweet. I've heard good things about Gu but have yet to try it.

Strawberry Clif Shot Bloks are awesome. They also have a Black Cherry flavor which is pretty good and has some caffeine in it. Like KSH said, they're easy to eat while riding. The Jelly Belly beans taste good, but they're pure sugar -- they give me a rush and then I crash.

For bars, I'd say Clif Bars, hands down -- chocolate chip, peanut butter, and black cherry almond flavors. I've only tried Luna Bars once (Dulce de Leche flavor) and didn't like them.

Aside from cramping, as you guys mentioned, drinks that only have very simple sugars will make your blood sugar shoot up and then plummet. If you use a sports drink or gel that has different types of carbs (which are metabolized at different rates) effect is more subtle, rising slowly and then tapering off. That's why it's also good to mix different carbs when you're eating before a really long ride -- like wheat, corn, oats, rice, etc.