Looking forward, I see a problem with the current naming for User I/O.  I see VISIBLE/INVISIBLE as being more appropriate for variable scoping and OOP access control than for input and output.  I propose a few simple replacements:

Simple input:
  ASK <prompt> <var>
Advanced input:
  LISTEN FOR <var>
Simple output:
  SAY <expr>
Advanced output: (no automatic newline)
  TELL <stream> <raw output>

For the last one, it requires string notation, which I propose below:
  "This is a string" / 'This is a single quoted string'

I propose that these strings follow standard perl conventions:
  * Variable interpolation with ${}
  * Escaping with \
    - Standard characters (\n, \r, \0)
    - Negate special characters (\\, \", \')
  * No interpolation within ' '-strings

 --- //Kyle, 2007/05/29 05:11//
----

I suggest WUT? instead of ASK, functioning as fgetc.
<code>
HAI
BTW LOL
CAN HAS STDIO?
I HAS A VAR VAR2
IM IN YR LOOP
	IZ VAR2 NUTHIN KTHXBYE
        VAR PLUS VAR2
        VAR2 WUT?
IM OUTTA YR LOOP
VISIBLE VAR
KTHXBYE
</code>
 --- //sokk, 2007/05/29 08:23//

---- 

Someone else used TXT ME for input, and it seems thats what people like to use:
  TXT ME VAR

I agree that VISIBLE and INVISIBLE might not be the best choice for output. Something else is needed. 
  ISEZ <value>

----
''TXT ME A'' has been replaced with [[examples:GIMMEH]], with your permission.

And ''VISIBLE'' and ''INVISIBLE'' were chosen for their ubiquity in simple, BASIC-like programs. LOLCODE is not that sophisticated. Objects? Control over scope? I think we grew up in different decades. ;)
 --- //Adam, 2007/05/29 13:13//
----
I know some folks have promoted LOL for setting a variable, but I think it works better as an output, especially if you allow '!' to be a CR/LF:
<code>
HAI
CAN HAS STDIO?
I HAS A VAR
IM IN YR LOOP
	UP VAR!!1
	LOL VAR!
	IZ VAR BIGGER THAN 10 O RLY?
          YA RLY
            KTHXBYE
        KTHX
IM OUTTA YR LOOP
KTHXBYE
</code>

----

<code>
HAI
  I CAN HAZ LIBARRY "stdio"?

  I HAZ numbar

  W00T "Gimmeh a numbar, kitteh!"

  GIMMEH numbar

  O RLY? Iz numbar BIGGURTHN 5
    YA RLY
      W00T "Numbar biggurthn 5"
    LOL

    NO RLY
      W00T "Numbar iz lamer"
    LOL
  LOL
KTHXBYE
</code>

 -- //Alan!!111//