The BSAC one is pretty small

This is the logbook I've got

http://www.scubapro.com/products/accessories/passport_log/passport_log.asp

It's almost exactly the same size as my passport.
I really like it because it's small, waterproof, and gives
you lots of room to write details and comments.
Even though it's pages are waterproof, i still keep it
in a Ziplock bag to keep it from getting soaked or saturated
on the dive boat.

you should be able to buy it anywhere you can buy Scubapro
products.  there is a dealers link on that above web page.
I think it was about  $10-$15 US. (but not sure.)

I did a search and this is the first dealer I found
that sells it.  I'm sure you can find more.
http://www.yachtdiver.com/sp/acc/misc.shtml

I'm really happy with it as I didn't want to haul
around a huge binder type like the PADI brand one
and other brands were paper and got wet easily.

this should help.

-Mike

Naui's format was exactly like that, but I believe they stopped printing
them a few years back.  

What I use are spiral-bound index cards, available from my local office
supply store.  

Because they're made of heavy index card stock, they're more rugged,  
more wind resistant and water resistant.  While they're technically not
waterproof, than normal lightweight paper (including the waterproof
stuff), they do tolerate damp hands, water dripping from your hair, etc,
because of the heavy paper stock.

Note that these are just simple lined cards, so you'll have to invent
and use your own "logbook" data format.  IMO, this is worth it, because
this also means that you can easily dedicate a page anytime you want to
draw a map, tear it out of the book for some other purpose without
guilt, etc.  Here's an example page (note that you probably won't
understand all of my shorthand):

http://www.huntzinger.com/photo/2000/log2000-09-23.gif

The specific place in the USA that I get them is through an office
supply store retail chain called Staples (www.staples.com).  The proper
product name is "Oxford Spiral Bound Index Cards" and the below URL
should give you more information:

http://tinyurl.com/i4cx

They're roughly US$2 for a 50 page notebook, and they're available in
both 3"x5" size and 4"x6" size (I use the 3x5).  Just toss a cheap pen
through the spiral binding and the whole thing into a ziplock bag.

-hh