Generating alphanumeric gibberish?

What's a simple (preferably loopless) way to generate a large amount of alphanumeric gibberish? Any language is acceptable.

In PHP, I thought this would be perfect:

hexdec(mt_rand(1.e999999999, 1.e9999999999));

But it doesn't work due to restrictions on the length of int. :(

>>19
I got it to run in about 3.9 seconds.

(time (for ((i (in-range 1 100000))) (gibberish 100)))
cpu time: 3873 real time: 3874 gc time: 16
(time (for ((i (in-range 1 100000))) (gibberish 100)))
cpu time: 3924 real time: 3935 gc time: 4
(time (for ((i (in-range 1 100000))) (gibberish 100)))
cpu time: 3912 real time: 3911 gc time: 12