GINA only reads the log file and is incredibly helpful. Helps with setting spawn timers, notifying you when your spells/debuffs wear off mobs, when buffs wear off or are dispelled, etc. Also helpful for some raid encounters.
GamParse parses the log files and attempts to show DPS live (and/or for historic fights) and breaks up your log file in a more easily readable fashion as it separates out fights, tells, auction, etc, in specific sections/tabs in the application. There are other parsers (Yaulp comes to mind?) that you can find if you're resourceful, but GamParse is the most commonly used, I think.
There are also map applications which only read the log file (p99 compliant) and plot a point on an map image when you /loc in game, example here:
http://mappa.000webhostapp.com These apps are good for people who are directionally challenged (/raises hand)
I never got much into the textures and similar but there are also custom UIs that you can check out (I prefer the stock UI, personally).