Is there any free/paid Windows emulator for Mac OS X?

I am new to Mac and I am looking for a Windows emulator for Mac OS X. I want to use an application which is not available for Mac. Please recommend the strengths and weaknesses (including cost) of the various options available.

Wine

You could try Wine and use the Winebottler frontend for installing common Windows software.

With Wine isn't 100% compatible with all windows programs, so consider yourself lucky if all your applications work.

Virtualbox

Virtualbox is a PC virtualization software. You'll need to install Windows as a "Guest operating system", which requires a Windows license.

Virtualbox is compatible with all Windows software, but has limited support for hardware 3D acceleration.

Boot Camp

For 3D games you'll need to use Boot Camp.

When using the term "emulator", it is important to distinguish between something that acts like Windows to applications (like Wine/Crossover) and something that acts like a PC to Windows (most of the other solutions) so that Windows can be installed.

Wine (Free)

I highly recommend Wine, which allows for running Windows applications without actually emulating the whole Windows OS. I don't know how well it works with 3D stuff. I would also not recommend compiling it yourself. You do need to install the Developer Tools, included on your computer's install disc. I would recommend Winebottler, a free binary installer that also allows you to turn a Windows executable into a simple application that launches in X11.

Wine (and Crossover) do not require an actual copy of Windows installed on your machine.

Crossover ($39.95)

Professionally supported enhancement of Wine

Q (Free)

Q is a great lightweight CPU emulator for OS X. Oddly enough, it runs on PPC Macs, in addition to Intel Macs. It supports emulating x86, x86-64bit, PPC PowerMac, PPC PREP, SPARC32, MIPS, and ARM processors.

Virtualbox (Free)

Virtualbox is not quite as lightweight as Q. It supports x86 and AMD processors. It allows multiple operating systems to run on your computer.

Boot Camp (Free) - Comes with all Intel Macs

I would recommend Boot Camp for 3D stuff. I haven't actually installed it on a Mac, I've used a friend's computer, so I can't help you with installation. As with anything Apple-related, it should be pretty straightforward. It also runs really well.

QEMU (Free)

Another lightweight emulator. This one is somewhat confusing to download; I think you have to compile the emulator by hand.

VMware Fusion ($80) by VMware

I don't use VMware (I like the free stuff), but I've heard good things about it.

Parallels Desktop ($80)

I haven't used Parallels, but it used to come for free with a new Mac. It still may, but I'm not sure.