Mac Research is a site devoted to folks who use macs in their research. Excellent source of good stuff.
Freeware that we love

Cyberduck
Drop Copy

Stuff that doesn't cost much & is really useful
Notebook Rocks!!!
We have tried a lot of database applications. Here's a simple, powerful one that doesn't even look like a database application but really is.
You can squirrel all sorts of stuff away in your note book, and you can find it again later.
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Sente (iTunes of reference managers, you'll pitch your endnote when you try this out.
Stuff costs a lot & is really useful
IPlabs
Is software developed and distributed by Scanalytics. We use it all the time, it runs well on OSX, though it is long in the tooth and needs a major upgrade to really take advantage of the new OSX. It controls a wide variety of shutters, stages, and cameras. More importantly, technical support is helpful and just a phone call away. They were bought recently by BD biosciences, and we dearly hope this doesn't mean the end of their Mac support. We're holding our breath.
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Huygens software
This is fantastic software for image analysis and deconvolution. It is developed and marketed by Scientific Volume Imaging and runs on Unix platforms including OSX.
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