I use Kiefer swim workouts online, white 3×5 notecards, and a snack size plastic bag. Very high tech.
There are plenty of good websites to pull workouts from: Kiefer and Speedo Pace Club are my two favorites. Speedo has workouts at varying levels of skill (including beginners!), while Kiefer tends to be for those more advanced.
And now that I’ve successfully diddled around, I’m now leaving later for the pool than I intended.