You can convert these following formats to PDF for Free:

DOC
PPT
XLS
JPG
GIF
TIFF
RTF
PPS
HTML
BMP
PNG
EMF
TXT
PUB
WMF

Click here for web service

I use PDF Creator.

Just install it on your computer, and it shows up like a printer. To create a PDF from any program, just choose PDF creator as your printer, and it will save it as a PDF instead of actually printing it.

Thats funny. I found this today after I had PM'ed Rorshach.
He did show me another program that was very nice but a tad expensive.

SJ

You could also try CutePDF Writer, the price is right - free.

I use Mac OS X and the included Preview application will let you save as a PDF as well.

Or if you have openoffice.org you can save directly to pdf. Great feature!

One could also use pdf995 to make pdf files from anything you can print on the PC. It is free but a bit annoying. If you choose not to buy the software, it will let you use it for free. It will, however, bring you to their website after each use to suggest that you buy it. Basically it gives you an ad with a slight time delay each time you use it for free. I like it when I'm on a pc since it seems to make fairly small files with good quality.
pdf995.com

On my Mac I use the built in pdf maker.