I've got the following keymap in vim:
inoremap { { }<Esc><BS>i<CR><CR><Esc>ki<Space><Space>
If I want to type a literal { without the other characters, how can I do it?
The way to enter a literal character in vim is to use Ctrl-V.
In your case, when in insert mode, you'd type Ctrl-V followed by {
Note also that there exist several brackets oriented plugins that detect the context in order to not expand things like { in comments or string contexts. lh-brackets, that I'm maintaining, also has a enabled/disabled feature, toggled on the trigger key.
Otherwise, for the punctual disabling that doesn't match recognisable contexts there is CTRL-V as ffledgling has told you.
NB: the idea behind context detection is to match the result of synIDattr(synID(line('.'),col('.')-1,1),'name') against 'comment\|string\|character\|doxygen' (see lh#map#*context*() functions in lh-brackets), and have your map-<expr> expand to either { or {} + cursor movement that doesn't break redo + other things possibly.