Ubuntu and it's derivatives are indeed the most popular, and probably the easiest to use.
Try http://distrowatch.com/ -- read the information about a few of them, and decide from that.
For some reason, they have FreeBSD on there; it's nothing to do with Linux but there you go.
Personally I use Arch Linux: http://distrowatch.com/table.php?distribution=arch
I'm thinking of trying a source distribution (that is, one you compile & build yourself) and then a proper Linux From Scratch (I got a working kernel and everything, but I didn't build the userland myself and I want to do that).
and to mention because it hasn't been yet, if you still want to use windows then dual boot can be a bad thing so you can use a virtual machine and put linux on that or better yet get Cygwin http://www.cygwin.com/
runs within windows.
Sure, if you enjoy getting sodomized by hardware markups.
Has anyone else noticed a decline in the Cygwin's stability when running programs from a regular command line? If you go back and forth between several consoles Cygwin tends to crash a lot with stack overflows.
Or, just throwing out some random ideas here, you could partition your hard disk, install Linux and then switch between Linux and windows.
Better yet, you can use an emulator like Qemu in fullscreen mode and it would basically be the same as using the guest OS, but a little slower. Even better still, you can use KVM (if your hardware supports it (and unless you're using something very exotic, it probably does)) and achieve very nearly native performance.
Double booting is probably the most reliable way to run two OSs at once. Emulation can sometimes incur unexpected problems, and the compatibility is not as high.
Ubuntu seems to be the most popular desktop Linux distribution. It is easy to install and comes with a nice collection of software. It's relatively small, too. Ubuntu 10 is currently in beta testing and scheduled to be released at the end of the month.
Another distribution worth considering is Fedora. It has a longer release schedule but aims to marry the latest available technologies. Personally, I like Fedora but the installation is really large. At home I run everything in VMs, so I wanted a smaller host OS.
For virtualization, I prefer and recommend VMware Player. It's free and works great. I used to use Cygwin, because I prefer Linux development environments, but running VMs has additional benefits. For example, backups and redeployments are just a file copy away. There's so much software out there and just as many untrusted sources, that you shouldn't just download and install everything that you want to check out. With VMs, you have an "expendable" OS to toy with.
On the down side, performance is a little slower. I would recommend 2 GiB to run VMware Player; performance is then acceptable for workstation-type tasks, such as software development, email, document manipulation, photo editing, etc.. It would not be suitable for more memory/graphics-intensive applications, such as games.
Grey Wolf, I agree completely. Consider a backup strategy for a dual-boot machine, for example. Removable hard drive bays/trays are not terribly expensive and disk space isn't either. iStarUSA offers some great removable enclosures.
Actually, if it weren't for game support such as Left 4 Dead on Windows, I would absolutely NEVER use Windows. As for a preference in Linux, I suggest Fedora for simplicity, modern, and easy. I fail to honestly see the advantage of Ubuntu (or Debian for that matter) over any of the others that compete with it.
I do NOT suggest Gentoo unless you're wanting more experience in the structure of Linux and source code based maintenance while in a secure environment. It gets terribly slow and must be optimized and configured almost perfectly to get all of the functionality out of it.
If you were to do this, I would just go and print the LFS guide and have a ball with that since it's probably twice as more educational although twice as complex.
FreeBSD and other BSD children are all rather good. The problem is it's drivers are not as developed as Linux's and it's development is a lot slower because of a smaller community. I will say however, that even with that, it is a relatively good choice and does its best to keep up.
Minix was originally used for teaching and educational purposes. Today, Minix3 is a modern, still in development kernel based OS which is stable, easy to learn, and fun. It is Unix based (originally it was at least).
I just installed Slackware 13. I haven't really used it yet but I'm not sure I like it very much. It feels like I have to fight it to get it to do some things, like change the keyboard map.
Actually, if it weren't for game support such as Left 4 Dead on Windows, I would absolutely NEVER use Windows.
Lucky for us, VALVE is planning to port the Source engine to Linux. They already ported it to OSX, Linux can't be far away.
The problem is it's drivers are not as developed as Linux's and it's development is a lot slower because of a smaller community
Today, Minix3 is a modern, still in development kernel based OS which is stable, easy to learn, and fun
Minix is still only useful for teaching purposes IMO. Have you ever used it? There are some very good ideas in there (reincarnation server, boot monitor, etc.) but the lack of a desktop environment for it (the closest you can get is bare X11, which is not exactly "modern") means it can only really be a teaching operating system).
i am new to linux and i have tried several, but find ubuntu (on my Main pc) and xubuntu(on the net book) to be the easiest to learn. i use xubuntu on my netbook because it seems to run faster.