I'll address your full list later when I have more time, but some quick ones I can address with little research:

THE Rename - A batch file naming utility.
OS X equivalent: Terminal and the many unix commands to do this. Learning how is a great way to get used to Unix commands in general, and the knowledge is highly portable. With Cygwin on Windows, such info is even usable there. I haven't used a GUI app to mass rename files for a long time.

Sony Ericsson phone suite
OS X equivalent: iSync/Address Book/iCal. Built in, and iSync has always supported SE phones very well. The old T68i was also the phone Apple used to always demo iSync way back when.

Openoffice.org - as you already noted, has an OS X version. Give the trial of iWork a shot though, it's really nice in a lot of ways, and is also compatible with all the MS formats along with spitting out PDF and such.

Picasa - Exists for OS X now, so transitioning should be easy. Give iPhoto a shot, but it all really depends on what you need out of a photo app. iPhoto can upload to various services with plugins if thats your big tie to Picasa. Really the only big benefit I can see in migrating beyond the native OS X app feel is the iLife integration. Photos in iPhoto show up in iWork for quick addition, in iMovie and iDVD for slideshows, and so on.
*edit* Looks like Picasa for OS X is not out yet, but news from Macworld in January did say it is coming. Google provides the Picasa web album uploader for iPhoto now.

uTorrent - OS X version I believe, but look into Transmission.

GMail Notifier - I've seen some. Look for one with Growl support for an array of notification options. GMail over IMAP to Mail is always a possibility too.
*edit* Google has their own too. http://www.google.com/mac/