Can anyone recommend a really good one?

http://www.openoffice.org/ the draw program can export PDFs.

I believe Google Documents can do it online for you, but I also use Open Office as mentioned above.

Another option is ps2pdf.
Take any program, print to file. This should be a postscript file. Then run ps2pdf to convert it to pdf.

For generating PDF's on the fly, I like PDFBox. This lib will let you do just about anything (including embedding TOC, javascript, links, etc...).

Yes, OpenOffice is a good and free choice for converting text documents into PDF.

However if you look for more professional features (like encryption, digital signature, document version management), it must get stated that there goes nothing about the Adobe products (even they are pricy).

www.primopdf.com Free