a 3-ring binder with note paper, everything since is just logged into my PC, where I suppose I could print it out if I had any reason to. My "early" dives had tons of info...wt, air consumption, all that stuff...but now it's mostly just location, date, max depth & time, # of customers/students and anything of interest I saw on the dive. Since it's all (the last 7 years) tropical swimsuit & t-shirt diving, I don't use wts or wetsuits anyhow. I have one "teaching site" where I've done ~1,050 dives, so there's not a good reason to write down the same fish 1,050 times!
The main exception is when I dive on a day off...I try to find a new site & I'll make plenty of notes in my computer to reference later, especially if I want to consider it as a site for future customers.
Oh...and as far as "what's a dive?" (I know this was asked early in the topic; I haven't read the intervening answers) I've typically heard 5m (16') and 20 minutes or more with at least 10 minutes SI. One could do roughly 48 dives/day using this "formula" (30 minutes per dive "cycle" assuming they had someone there to hand them a fresh tank) but I'd never think of those as "real" dives. I've never tried to "pad" my numbers by doing these kinds of dives...normally my dives would be: working, 8~40m (27~130') for 30 minutes to an hour, with an SI of 40 minutes or more. Day off dives would be from 8~you-don't-want-to-know-how-many meters, for 40 minutes to 1:30.