I love Pitbull for unit frames. Tiptac is a nice, compact little add-on that improves your tooltip Shows target's target, talent spec, and even buffs in a nice clean window that doesn't dominate screen space. Quartz is a good casting bar add-on with a raft of options.
It's a very good idea to get a bag add-on which will make managing your inventory much less of a headache. I use Combuctor, which has the usual bells and whistles- one single bag window, ability to search by name, and bank viewing anywhere. It'll even let you view the bank of other characters, tell you how many of an item you have on your current character and all others on a realm, and it will allow you to filter inventory items by type (trade items, consumables, etc.) and sub-type (gems, recipes, etc.) and by grade (common, rare, epic, etc.) It's a huge help.
Finally, for a hunter, you should look into a range add-on, which will show how far you are to a target. I'm using RangeDisplay, which can show the distance to your target, to your focus (important for healers), and on your mouseover. Ranges are shown as text with a certain amount of precision: 15 to 20 yards, for example. This is limited by the WoW client itself, so all range addons are working with the same restrictions; they just show the data in different ways.
