Codekit for watching all the code and compiling everything anytime something changes. Particularly useful with includes for LESS or SASS. But also useable with CoffeeScript, JavaScript minification and so forth
Tower this is by far the best UI i have found for git. i've bought GitBox and tried the GitHub Mac client too, and used the command line.
VirtualHostX such a lovely tool so nice to be able to whip up a new local website in a matter of seconds
Editing: i use Espresso but i can't honestly say if it's better than Sublime Text or Coda. I use it because i used CSSEdit which is now a part of espresso and i find that to be essential for what i do. I will say that if you are typing HTML AT ALL you need to be using zen coding which is supported by all these editors.
Merging: i think my preferred merge tool is DiffMerge but i recall that the xCode one had some features that i preferred. Not in love with any merge tool so far.
Diffs: i use Kaleidoscope - i have never upgraded from version 1
i use iTerm2 FWIW, very minor improvement over basic terminal (tabs, essentially)
i use a plugin for the finder called Go2Shell
i use MAMP so that i can run Wordpress on mySQL but that prolly won't matter to you
i use Safari with Developer tools enabled (preferences->Advanced tab->tickbox on bottom)
i use Firefox with Firebug plugin when i really need to debug JS and AJAX
jQuery, Bootstrap, of course. I want to try mixing Bootstrap with angularJS using this
FontAwesome and The Noun Project are great. i like TypeKit for custom fonts, they can really make a difference to a site. Basically, because of retina displays & responsive design it seems better to me to eschew graphics in the basic site design (as opposed to D3 or whatever, where the graphics are the content). And because of this typography / iconography (and color, obvs) can help a great deal.