In another thread I got alot of valuable tips about how to run my mac efficiently. MacJanitor and onyX were two of the many good freewares.
Do you know any other cool/good program that you think everybody should have?

Thanks.

VLC is a good for instance.. You find it here..
http://www.videolan.org/vlc/index.html

I hope you weren't just asking for utilities, or system apps -

Audacity
http://audacity.sourceforge.net/
A slick little multi track audio editor. Easy to use. Powerful. Free. What's not to like?

GIMP
www.gimp.org/
Image manipulation. Okay, so it's not quite Photoshop, but it's better than Photoshop 3, and most of the features of Photoshop 4, and some features of 5 and 6. And once again - Free.

Open Office
www.openoffice.org/
www.macdevcenter.com/pub/a/mac/2003/02/07/x11.html
M$ Office Replacement. Now that the Mac OS is Unix-based, X11-capable, let the open-source games begin!

I have the audacity one.. the other two? Great! I had no idea there was an office option.
Do you know if files open alright on PCs?

Thanks

Check out this site:

http://www.missingmanuals.com/cds/

This website has both freeware and shareware. It is the site of all "The Missing Manual" books. Lots of stuff... some good stuff for iMovie - Amadeus II, Snapz Pro X, Sound Studio.

Missing Manuals... a must for all Apple newbies.

Open Office is basically the open source vesion of Sun's StarOffice. You can find info about StarOffice here:

www.sun.com/staroffice/

And yes, it seems to be very compatible with Microsoft Office, allowing you to open, edit and save to all the Office document formats. It also lets you save documents as PDF's without having the full version of Adobe's Acrobat.

Another bonus is that all three of these apps are available for PC's and Linux boxes as well. So if you like the interface, you can get the same free goodness no matter what OS you use.

More stuff... utilities, iMovie, etc.

Both freeware and shareware

http://www.macupdate.com/

HackTV and SimpleVideoOut from Apple are great little things. They help me capture and output video over Firewire on small Macs without the overhead of the whole NLE.

It's inexpensive shareware, not freeware, but I really like BTV Pro (http://www.bensoftware.com/btvpro.html), which is a little program for capturing and displaying video on a mac. One of the nice features is that it will display full screen, full frame video at any size and aspect ratio desired. I use it on my Powerbook as a monitor to display anamorphic 16:9. I realize this isn't a true substitute for a real NTSC monitor, but it's still pretty handy for judging focus and framing. I use the monitors control panel to adjust gamma to something closer to NTSC.