Easyfind - better search in some situations than Spotlight
VLC - media player plays just about everything. A bit too much at times so I also use NicePlayer.
CarbonCopyCloner - make a bootable backup of your hard drive
The Unarchiver - compressed file expander for many formats
LiquidCD - optical disc burner
XLD - CD ripper. yes, itunes does this, but this tool does multi formats at once, better naming than iTunes, file conversin, formats itunes does not support. etc.
All the above are free or donationware.
I have somewhere between 50-100 applications on my computer, many of which I only use in specific circumstances so a large part of recommending depends upon what you mostly do with a computer. Some of the ones I use most heavily you might never use at all so you're inviting a hodge-podge of recommendations.