My favorite kind of game is the Role Playing Game (RPG). This category can cover some very different kind of games, but the type of game I'm talking about in this entry is one that usually contains about 60% combat (be it 1st or 3rd person shooter, turn-based, etc) and 40% dialogue -- that is to say that a large amount of the plot is advanced by the player character (PC -- the character that the player controls) interacting with non-player characters (NPCs -- characters run by the computer or programming of the game). I love these kinds of games because they usually have extensive background, a large world/universe in which the game takes place, complex plots, opportunities for interesting interactions with the NPCs who tag along with the PC (including opportunities for romance!), and the possibility of multiple, sometimes radically different endings based upon the choices that the PC makes in the game. In many of these RPGs, the gamer is allowed to choose the gender of his/her character, and is sometimes given the option to customize (occasionally with great detail) the appearance of his/her character. So, now that I've given you the context of the type of game I'm about to talk about (so you non-gamers can understand what I'm saying), I'll give some examples of interesting ways race, gender, and sexuality have played roles in these games.
1. Race
One of the RPGs I was playing this summer is called Dragon Age. It was one of those RPGs that allowed me to customize my character appearance. I made my character (who I named Victoria) brown-skinned, with dark hair, and brown eyes. However, Victoria's background in the plot of the game is that she was the daughter of two nobles. They were both white. I played through the opening sequence of the game, musing to myself if any of the NPCs were going to notice that Victoria is the black daughter of two white parents. Of course they didn't, but the thought amused me. My point in this story, however, is that while the player has the option to make his/her character any skin color he/she likes, the majority of the NPCs I ran into throughout the course of the game were white-skinned.
2. Gender
I have to admit that I used to play a game called World of Warcraft (WoW). It's classified as a massively-multiplayer online role playing game (MMORPG), but what that means is that it's an online game that a lot (and I mean literally millions of people play. It's not the same as other RPGs, since it doesn't contain the dialogue aspect that I discussed above, but that's what they call it regardless. Anyway, the point is that there is a notable phenomenon of men who play female characters in this game. It is joked that if you see female characters in the game, they are actually G.I.R.L.S. -- Guys In Real Life. Men's reasons for playing female characters vary. Some say, "If I'm going to be playing the game for hours, watching the backside of my character, I'd rather it be an attractive backside." Some prefer the character design of the females over the males. Some don't have a reason at all. Some men flat-out refuse to play male characters, while some men refuse to play female characters. There are, also, women who play male characters, but it is rather more rare. Many women say they prefer to play female characters because they find it empowering. I played both male and female characters equally, but my decision was made based on character design.
The interesting part of this all, however, is that while it was widely known that a large majority of the female characters in WoW were in reality played by men, other players still assumed female characters to be played by females. As I played both female and male characters, I noticed a significant difference in the way I was treated by other players based on whether my character was female or not. While playing a female character, other players would give me money or items for no real reason, or would be more patient in explaining aspects of the game. Sometimes (more often than I'd like to admit), I was propositioned for nude pictures (an odd thing to ask for, if you ask me, considering that chances are very high that I could actually be male). If I was playing a male character, other players were much more likely to call me a fag and yell at me if I played poorly.
My point is, that while anyone of any gender can play either male or female, and all the players know that the gender of a character did not reflect the gender of a player, female characters were treated according to patriarchal (usually of the "benign" variety) norms.
3. Sexuality
This summer I also played a series of games, Mass Effect 1 and Mass Effect 2. In this game, the player controls a character named Commander Shepard, and the setting is in the future, in space, and so therefore many NPCs are non-human. The player, again, has the choice to play a male or female character, and to very specifically design the character's appearance. I choose to play a female Shepard because I've found that RPGs are far more interesting when one plays female characters, because NPCs are programmed to react to you differently than they would to a male PC. In Mass Effect 1, a female Shepard can pursue a romantic relationship with either a human male crew member, or with a female alien crew member (well, technically, this alien species is mono-sexual, so male and female don't make sense in this context, but the point is that the character appears female-bodied, so, for all intents and purposes, is considered female). However, a male Shepard could only pursue relationships with females (human and non-human). This, unfortunately, is not uncommon in RPGs of this ilk. It is assumed, I think, that there are no gay male gamers, so there is no need to offer the opportunity of gay male relationships in the game. Lesbians, however, become objects of male desire within the game, and the opportunity to form lesbian relationships within the game is being marketed to straight male gamers, not to possible lesbian players.
Apparently, however, the creators of Mass Effect 1 received a lot of flak for including lesbians (but not really) in their game. So, in Mass Effect 2, female Shepard is confined to males, and male Shepard is confined to females. The interesting thing -- and I also think ridiculous and hilarious -- is that while Shepard is confined to romancing the opposite sex, Shepard is not confined to romancing only humans. Yes, that's right, you can sleep with lizard men, as long as they are lizard men.

Yep. That happened in my game. I banged that guy.
I think this has something to say about heteronormativity: better for your relationships to be cross-species but heterosexual, than for you to sleep with a member of your own species who is the same gender.
Mass Effect 3 is coming out soon, though, and thankfully, I've heard, both male and female Shepard can be as gay or straight or xenosexual (I made that up, but I think it's pretty good) as they want to be.