I mean, if you want a specific tea with hella caffeine, Pu Erh is the mother of all black teas. You wil find that it tastes like dirt. This is because it is somewhat fermented underground, strengthening/changing its energizing functions.

Similarly, Yerba Mate is very energizing and I believe it is technically "caffeine free" - but only because it has a stupid amount of a caffeine-like compound called "mateine".

I suspect that you'll run into the same problems that you do with coffee though, in that they'll keep you up longer than you'd like.

In my opinion, the ideal type of tea for this - and any other number of purposes - would be a nice Oolong. Falls between Black and green teas as far as caffeine goes, and can be re-steeped up to 6 or so times. What I did in school was get a travel mug with a french press built in, put in a serving of oolong tea leaves, and go back to the Starbucks or food court for (free!) hot water refills every time I needed it.

At the 6th resteep, there will be virtually no caffeine content left, but still some flavor. It's a good way to gradually decrease the amount of caffeine you're ingesting over time.

I don't remember if you're in the US or not, but I highly recommend Strand Tea if you are. I live a town away from them now, but I've been buying from them since I started/ran the Tea Club at my college 4 years ago. Really solid prices, a good selection of a bunch of teas, honest people, and the shipping is fast and reliable - I usually got my packages 2-3 days later when I lived in NY. They should also have travel mugs that will work for infusing for sale too. If not, get a Bodum french press travel mug on amazon - I think mine was like 15 bucks when I got it. Still have it somewhere.

An 8 oz. Bag of tea is like 100 tsp, if I remember correctly, which would be up to 600 steepings of Oolong. At 10 or so bucks, that's stupidly cost effective.

If you buy from Strand Tea, my favorite Oolong of theirs is the "Three Treasures" - really unique, and has a tremendous depth of flavor that changes with each steeping.