Paste in insert mode?

While in insert mode hit CTRL-R {register}

Examples:

• CTRL-R * will insert in the contents of the clipboard
• CTRL-R " (the unnamed register) inserts the last delete or yank.

To find this in vim's help type :h i_ctrl-r

If you don't want Vim to mangle formatting in incoming pasted text, you might also want to consider using: :set paste. This will prevent Vim from re-tabbing your code. When done pasting, :set nopaste will return to the normal behavior.

It's also possible to toggle the mode with a single key, by adding something like set pastetoggle=<F2> to your .vimrc. More details on toggling auto-indent are here.