MY QUESTION:   How can I -- an experienced pro in my field (voiceover
direction) -- more effectively present my credentials to a larger
group of potential video game producers; i.e., the individuals
actually designing the games (or supervisng the game design) at game
development companies?

BACKGROUND:  I'm an L.A.-based member of the Directors Guild of
America with more than 20 years experience in directing actors in
voiceovers for films, TV, commercials and animation. Have cast and
voice directed over 2000 episodes of network and syndicated cartoons,
and have extensive background in directing voices for video games
*DreamWorks, Infogrames, Konami, etc.)

In contrast to the world of film and TV animation -- where the studios
are fairly centrally located, the producers' names appear in the
credits, and the producers themselves are reasonably accessible --
game producers are almost invisible.  It's a different culture.  The
game industry itself is geographically scattered, names of individual
producers are seldom publicized, and the intrusion of the outside
world -- including those who would pitch their services -- is not
especially welcome.

This In spite of the presently up-tick game business economy (already
larger than the movie business) where increased competition between
game developers for the hot games of the year requires ever greater
polish in every aspect of production, including the acting.

Fairly recently I rented the subscription list of a video game
industry trade publication to use in sending out a concise but
eye-catching direct mail piece promoting my services.  Subsequently, I
learned that the magazine may be read more by game programmers (the
technicians who devise the game machinery) than by producers who would
be concerned with the voice acting.  In any case, the response --
although it paid for the mailing and the list -- was tepid.   I'm also
on a couple of websites that list specialists to the game biz, and
will soon have my own website doing the same.

A generalization:  Many game producers tend to be a bit on the "geeky
" side -- somewhat introverted and averse to anything that smacks of
pitching.   "Go way, man. I'm busy."

I think part of your problem is that while you have done successful
voice direction for larger video game companies, my feeling is that
the smaller companies don't have the budget or development methods
that require voice-over direction.

From my experiences at smaller game companies, usually the programmers
or development staff hire voice-over actors and direct them
themselves.  The ones that can afford union scale wages for v/o talent
usually can't budget for things like v/o directors.  You may need to
retarget your talents to fit the needs of these smaller companies. 
Perhaps start your own talent agency?