It's a girl!
We went out for pizza and came home with a guinea pig.
After dinner, we ran to the pet store next door to buy some bedding to clean Fancy's cage. Right up at the register, they had a really cute orange-and-black guinea pig that they had just received from a local shelter. They were selling the guinea pig and her cage for $30. I asked the lady how much it would be for just the guinea pig, explaining that we already had a cage (and a guinea pig) and had been thinking about adding a second one (well, *I* had been thinking about it, since I knew that guinea pigs are naturally social animals and usually do better as a friend. Jeff wasn't as enthusiastic about the idea, though). The lady let me hold her, and after a few minutes she said, "Well, if you want her, she's yours." I asked how much and she said, "No, you can just take her. We just wanted her to find a good home." She told me that we could take her back the next day if Fancy and this one ended up not getting along. Even Jeff had to admit it was a pretty good deal.
They've been introduced now for about 45 minutes, and it looks like it's going to work out. There's a lot of squeaking and chattering and chasing and minor scuffles, but from what I read online, this is all perfectly normal as they get used to each other and establish dominance and all that. If they weren't going to get along, we'd know it right away--they would have started fighting right away (and the serious fighting, too; not just the minor "hey, I'm the boss here" scuffling).
I actually got Jeff to admit, before we introduced them, that he really hoped they got along because this new one was really cute. I think her name is Caramel (we haven't quite decided yet).