I've tried a lot of Linux distros over the last 13 years. I even did a stage 1 Gentoo installation, which I don't think they support anymore. Instead of reeling off a list, I would rather ask you what you hope to learn from a different distro. We all have enough spare computers and spare hard drives to install a bunch of stuff and never touch it again. In contrast, what would you want to keep at the end of a couple months? For example, lots of folks have mentioned Gentoo. It's easier than ever to set up a fresh Gentoo box, because multi-core machines are faster than ever at compiling. However it's just as much a pain to update when you have to compile X repeatedly or leave it behind. Nevertheless, Gentoo has one thing most Linux distros cannot offer as readily: out-of-the-box PXE and TFTP server setup. If you've been wanting to learn more about bare metal provisioning (a useful skill), Gentoo is the place to start. There is nothing quite as rewarding as the first time you trick one computer into installing a setup on another computer. If instead you want to learn more about keeping a server running while meeting business compliance, then I recommend CentOS. It's the open-source version of Red Hat Enterprise, which has a completely different daemon configuration system (one that I find a lot easier to use). Anyone can say "eww, it's not Debian-based so it must be evil". It takes only a few hours of exposure to chkconfig and some of their other command-line tools to realize, "wait, it's working and it's tight. I might accidentally get something done this afternoon." Crunchbang has something esthetically pleasing: cleanliness with a desktop. I recently installed it on a Pentium III 866 MHz laptop from 2000 or so and loved that it worked without any special effort and I could customize the desktop using only vim. While I had to download a 32-bit non-PAE version for a first-gen Centrino laptop to run it, I got that ISO directly from two clicks off their front page. Building, running services once you've built them, tweaking your interface to these events... they're all different goals. Heck, you may be more interested in trying Linux on different CPU architectures to learn how they differ and what that means for maintenance.
What would I want to keep at the end of a few months? Good question. I don't use my laptop a whole lot, its mostly used for when I go out on repair jobs. I'll have it with me so I can mount drives to back them up, format them or so I can troubleshoot issues online or download drivers and the like. Also I'll bring it to my buddies place for music, movies, etc... Really what I'm trying to get out of all the distros I try is to learn something new. I have my laptop to experiment with and that's what I'm aiming for.
Experiment, have fun, learn something new. This
Nevertheless, Gentoo has one thing most Linux distros cannot offer as readily: out-of-the-box PXE and TFTP server setup. If you've been wanting to learn more about bare metal provisioning (a useful skill), Gentoo is the place to start. There is nothing quite as rewarding as the first time you trick one computer into installing a setup on another computer.
sounds interesting. Would you care to expand at all?
Gentoo takes care of a good few parts more than Linux From Scratch, which is the ultimate in learning and I should've mentioned it earlier. One piece that it provides is a compiled set of preboot execution environment tools. The short explanation for PXE: it's a server listening for mewling, new bootups on the network. You can only have one PXE server per subnet. The usual configurations involve a PXE server listening for servers that just received their IP addresses from the DHCP server (usually your router in a home network) and running from LAN boot. PXE chills them mofos out and hands them to the TFTP server to download installer files. My day job involves tech support for a server automation product. One thing the product does is provisioning, and it uses a set of PXE files from Gentoo to install on bare servers.