If you've ever tried playing a spellcaster in D&D, it's a lot of bookkeeping. It really tempts you to computerize everything and stick with MMORPGs, at least when it comes to spellcasting (when you're a Fighter, nothing beats rolling that d20!). So, how do we solve that problem?
Well, honestly, short of creating a computer program for yourself (and somehow lug around your laptop with you to your games), there is no "perfect" solution. But there are some not-so-perfect options available to you. Some I remember reading from various message boards and some I came up with myself (although I wouldn't be surprised if some people came up with the same solution). So here they are, ready to be pirated for your game.
Psionic magic is perhaps the easiest of the magic systems since it uses numbers to keep track of your power points. For a high level game, just keep a piece of paper ready and you can jot down how many power points you've expended: 3 pp the first round, 5 pp the second, another 5 the third, etc. Unfortunately, you'll also have to do some mental math adding up all those power points. Another less bookkeeping method is to give yourself counters or chips or tokens. At the start of the day, give yourself an amount of counters equal to your power points. And then when you spend them, discard them into a pool. When you rest, get your tokens back again from the pool. This works for low-level games but not so good at high level ones, especially when your power points rise to three digits (alternatively, at that point, you can probably use Monopoly play money).
Paladins and Rangers don't have much spells to keep track of but that's not the case with Clerics, Druids, and Wizards. So how do you keep track of your spells? Well, one solution is to write them on cards, index cards, or use your spare CCG cards as proxy cards for them. Then your spells memorized per day is easily the cards in your hand and then discard them when you've spent them (as suggested from Book of Nine Swords: Tome of Battle for Maneuvers). This is good for low- to mid-level games but can be problematic at high levels. I mean at level 20, without accounting for bonus spells, a Wizard has 40 spells per day! 40 cards in your hand isn't a hand, it's a deck!
Bards and Sorcerers are easier to take care of compared to to Clerics, Druids, and Wizards. Personally, I just list their spells known and write down a number beside the appropriate spell-level. If you want to shy away from the pencil, one method you can use is to gather different colored counters or chips or tokens (or even spare change). Red chips could represent your 0-level spells, green chips your 1st-level spells, etc. Just keep stock of your chips and throw them into a pool once you've expended them. The only problem here is that you need to remember which color goes with which spell level and at high level games, you need ten different-colored chips. Well, for the latter, you can mix and match your chips with tokens. For example, a red chip might represent 0-level spells while a red token represent 5th-level spells. If you're not so color-coordinated, spare change might be your best answer: the lower the denomination, the lower the spell level. Or Monopoly play money again is a good solution but poker chips and game tokens has always had better appeal than paper.