Drinking green tea gradually over the day (carrying around a thermos, perhaps) seems to give most of the benefits while minimizing side effects, provided you like tea. The worst aspects of coffee & caffeine come from having a whole bunch at once, then spiking and crashing.
A nice tea is good for three to seven brewings, depending the type and your brewing preferences. I understand that the amount of caffeine in the pot falls by roughly an order of magnitude with each brewing. Thus if you like the tea but are concerned about the caffeine, just throw the first pot away. Many folks think the second has the best flavor anyway . . .
Herbal teas are also worth a try. I like rooibos and roasted barley. Korean grocery stores often have big bags of the latter ("barley tea"), and it's great iced. (Roasted barley is also used to add flavor to some darker beers.)
Here's another source: