<p>I can't seem to find any GUI framework's for as3 that are as good as any the applications I already see out on the web; Is this something most people code themselves or am I missing something in flash itself?</p>

<p>I'm looking for dialogs/windows, buttons, text boxes, combos, drop downs, menus, etc etc and the ability to extend the components to make new ones.</p>

<p>I'd also prefer it to be as3 but any others will do also.</p>

<p>May need to elaborate a little.. I'm actually looking for a framework to allow me to create my own GUIs in flash, custom skins, colors, styles, etc.</p>

Short answer:
Here is the
list of base controls
.
Long answer:
Yes, there are many controls (such as
buttons
,
text boxes
,
combo boxes
, etc) already built into Flash / Flex.
Here is
one tutorial
I've found helpful that gives a brief intro to using some components (buttons) without using Flex Builder.
If you use something like Flex Builder, you will get full access to these objects in a friendly drag-and-drop environment, however, it is not necessary to purchase Adobe tools to develop with these, so long as you're comfortable using something like FlashDevelop or the free command-line mxmlc compiler.
Check out the
fl.controls namespace
in Adobe Live Docs for a complete list of these base controls included in Flash / Flex.