What completion mechanisms are you using?

[senny]

What I like most about Emacs, is that you can complete nearly
everything. Until now i stuck to the bundled completions like dabbrev-
expand or hippie-expand to combine them. But when i look through the
emacs-wiki there is a huge amount of scripts available to improve and
extend the completion mechanism (like company-mode, icicles,...).
Because I have no clue where to start searching for the ones I like, i
wanted to ask you what extensions you are using and how they help you
to optimize your day to day work.

Regards,
senny