I've mostly switched to caffeine pills when I need caffeine (which varies, usually I try to go caffeine free). For me I find 100mg is a good amount, though if I could find 50mg pills I would try that. My preferred source is "jet alert" since I couldn't really find anything else that wasn't just 200mg.

Also, I always use an L-theanine supplement when I take caffeine, it's amazing how much it changes things. Instead of feeling all jittery and agitated I just feel less tired and more alert. This is roughly the equivalent of just drinking strong green tea.