INYAR  Oops! I meant to write "the developper is one of the most responsives"... Sorry about my quite bad English  
(Version 1.2.10)

INYAR  I've tried nearly every finance managing app available for Mac... and finally found out that MoneyWell was the best for my personal use.

The great thing about MoneyWell is the way it allows you to manage your budget : it uses the envelope method, so you put money in different "buckets"/envelopes and use it until the bucket is empty... you're not checking the way you spent your money after spending it (like in most apps). It allows you to really control your spendings, not just analyse them afterwards through reports and stats.

The UI is great. Yeah, there're still a few features missing, but the developper is one of the most reactives : about 1 update/week, answers to every question... The 1.3 is on the way, with scheduled transactions for example.  
(Version 1.2.10)

INYAR  I just finished my master's dissertation (in French) using Mellel. Mellel, in combination with Bookends for the bibliography, are the best things that helped me in writing my dissertation.

Among many great features and qualities, I'd like to underline some :

- Perfect stability : never crashed, frequent autosave... and not a single problem with a 140 pages document including PDF, images and tables.

- Power of autotitles for outlining and configuring titles format, including in the Table of Contents...

- Power of "Character styles", "Variations" and "Paragraph styles", and a lot of useful key shortcuts (F1->F8 for characters variations)

- Perfect integration with Bookends (and probably also with Sente and other bibliography softwares)

- Power of Search/Replace function, with regular expression, saving of search/replace templates and creation of search/replace sets. It saved me a couple of days of verification and correction.

I think Mellel is a must-have for writing all kinds of very regular/organized texts, like academic/scientific writing, novel writing, etc.  
(Version 2.2.7)

INYAR  As Mikuro said, Perian is a MUST-HAVE.

Since 1.0 and the support of SRT subtitles, it has put QuickTime back as my default video player. And with it, the ability to use all the comfort of applications as Frontrow (wich uses Quicktime). That's simply awesome, since Quicktime is by far (and logicaly) the most beautifuly integrated player in Mac OS X. VLC was great, but I just love to be able to launch Frontrow, to see the film going on in the Dock or all the smooth effects with Quicktime.

And all this thanks to Perian. Only. Because the codecs and video features supported natively by Quicktime is quite disappointing when you have to use it.

The subtitles support is just great, perfectly efficient and flawless. Nothing to do : it automaticaly detects the subtitle file.

What's more, the installation process can't be easier. And finally, it's free and open source.

Thanks a lot to the developpers !  
(Version 1.0)

INYAR  I've been using several different programs on Windows to re-sync my subtitles or correct the timings and, although there're plenty of that kind of "subtitle tools", I never found one who was as easy to use and as efficient as Sears. That's not complicated, but it's really simple to use it and it works perfectly. I corrected my subtitle in 10 seconds when I needed 10 times more on Windows.  
(Version 0.70)