Absolutely PERFECT running under OS X 10.6.4!

That Apple does not offer this capability bewilders me.

This is far far better than using a terminal script that will create a Ram Disk:

Buried in the manual pages for Apple's command-line disk-image-management utility "hdid" are a few instructions on how to use this command to create and mount a RAM disk. The process basically involves creating a mount point for the disk, using the hdid command to allocate the RAM for the disk, and then create a file system on the disk so it can be used and mount it to the mount point.
#!/bin/sh

NUMSECTORS=128000
mydev=`hdid -nomount ram://$NUMSECTORS`
newfs_hfs $mydev
mkdir /tmp/mymount
mount -t hfs $mydev /tmp/mymount
Copy this text to a plain text document (not rich text) in TextEdit, and save it with ".sh" as the filename suffix (i.e., "ramdisk.sh"). Then open the Terminal and type "chmod u+x " followed by a single space, drag the script file to the Terminal window, and press enter. This will enable execution of the script by the owner of the file (you).
After this is done, to run the script just open a Terminal window, drag the script to it, and press enter. The default value for "NUMSECTORS" in the script will give you a 64MB RAM disk, but you can increase this number if you would like. The number represents sectors, and there are 512 bytes per sector of RAM. To edit the script after it has the .sh filename suffix, right-click it and choose TextEdit under the "Open With..." menu.
You can also run a similar script in one line using Apple's "diskutil" and "hdiutil" commands, which result in a more user-friendly RAM disk than the previous script.
diskutil erasevolume HFS+ "ramdisk" `hdiutil attach -nomount ram://128000`
When run in the Terminal, this command does a number of things (note the single quotes are actually "grave accent" marks). First it invokes "hdiutil" to attach an allotment of RAM but not yet mount it since there is no filesystem on it yet. After the RAM is allotted, it calls on the "diskutil" command to format the allotted RAM and name it "ramdisk," which will cause the Finder to mount it under that name in the default mount point /Volumes/.
This may be a preferred method because it is simpler and allows you to name the disk by changing the "ramdisk" name in the Finder.

The comment below is misleading. It looks to me the RamDisk size can be quite large, at least 1/2 of physical RAM. The slider starts at 16 MB, it doesn't end there.

Cool little tool now that I have a pretty large amount of memory. Reminds me of the RAM: drive on the Amiga. Is there a way you could have the disk dynamically change size to the amount of free unused memory in the system? That way, you don't have to create a disk of a set size, it is just there and able to hold as much stuff as you have free ram...if the OS needs more memory, it takes it and the disk loses free space to the point that it is "full" if you have files copied in there. (Then it really would be like the RAM: drive on the Amiga.)

Is there a way for the files inside the ram drive to stay after a shut down or restart?
I really want to keep some specific programs/files in it but having to re-copy them every time is quite a hassle especially when i use those files often.

to Anonymous:

You load an application into a Ram Disk and it runs ultra fast

When I wake from sleep, I see the RAMDisk icon on the desktop, but it soon goes away. It does not then show up as a drive in DiskUtility or anywhere else. I have developed the problem I think after upgrading to 10.6.6 (from 10.6.5).

When I wake from sleep, I see the RAMDisk icon on the desktop, but it soon goes away. It does not then show up as a drive in DiskUtility or anywhere else. I have developed the problem I think after upgrading to 10.6.6 (from 10.6.5).