First of all, are you sure?
UNIX-ish operating systems (with OS/X being the exception) don't really seem all that laptop friendly to me. I use windows 7 on a laptop, (I've installed cygwin and its X11 server, now my laptop is rather like a wireless X terminal that I use to connect to real machines)
Have you considered something like that? maybe renting a VPS or using an old desktop machine?
If you've got a "beefy" laptop, you might actually do OK with something like vmware and installing linux in an emulator. In this case, look for a bare, stripped down version of linux. You probably don't even want an X11 server. (slackware, archlinux, gentoo come to mind)
I don't care for apple.. at all... but I do have an old macintrash running OS/X, it's pretty decent. You might consider an apple OS instead of linux, if you absolutely must install on a laptop and the emulator path doesn't work and you're more into the unix stuff than specifically linux (remember, linux is a flavor of unix)
Someone else suggested distrowatch, I second their opionion
I use gentoo here, I've used slackware, debian, redhat, archlinux, LFS, mandrake, etc.. For getting real cozy with linux, a bare distro, like archlinux or slackware is the way to go. (I don't think I'd like these on a laptop though..)
If you want to join a cult, debian is for you. Clients seem to like the RPM flavors, they're alright, but I find them to be rather bloated down, usually with a zillion "monitor" processes sucking up resources.
Each flavor is different, there isn't a "real" linux distro, LFS perhaps is as "real" as it gets (I did that once.. great for learning, but I strongly advise against it unless you've already had some experience)
Is it linux or general unix that you're interested in?