I'm extremely skeptical of the entire notion of choosing mates based on their intelligence. In my experience, intelligence is surprisingly hard to judge, especially as part of an initial impression. Anytime someone claims to choose a mate because he/she is smarter, or less smart, than he/she is, my overriding impression is that the person making the claim doesn't have the faintest idea what he or she is talking about.
Good point. Some people you think are pretty smart are just good at displaying one thing they are good at, such as verbal wit. They may be quite foolish in many aspects of life, including their ability to deal with other people, which is the one thing you're going to care most about in a relationship. Some people you might think are smart just crave admiration or worry about their inferiority, so they put a lot of effort into trying to seem smart. Some of the smartest people feel quite secure about it and don't feel motivated to show it off. They believe they get along better with others by keeping it to themselves.
Imagine meeting two men at a party. One makes a point of talking really fast, using big words, and dropping names of academic writers in a field he's studied and knows you haven't. The other man speaks at a normal rate, using ordinary words, and asks you if you saw a recent, popular movie. Is Man 2 smarter than Man 1? Well, we at least know he has more emotional intelligence. But if you had your heart set on finding an intelligent mate, you might go for Man 1. And good luck being happy with him. Substitute woman for man if that's what you are in pursuit of, but I can't help thinking women would be more likely to make this particular mistake. Note that if Man 1 is also the sort who wants someone less intelligent, we can predict an especially grim relationship.
That said, one very common way to find your intellectual equal is to meet your mate in college. You're surrounded by a large group of people who are roughly your intellectual equals. Now, you can choose based on compatibility and physical attraction. If you miss the big opportunity in college, or, wisely, you decide not to pair up so early, you can always go back to school -- for example, law school, though then you've got to want to marry a lawyer.
You could check your prospective mate's paper credentials: SAT score, IQ. Of course, some people are good at standardized tests and some aren't, and marriage is not a standardized test.
I still think the best advice is to seek equality in a marriage. I think we are good at recognizing when people are on our level and make mistakes when we want either an idol or someone we can dominate. Equality is a good principle all around.
By the way, my own parents knew the results of their IQ tests. (They met in the Army in WWII, and I think the Army tested them.) My father's IQ score came out one point higher than my mother's, and they had a very long happy relationship. They had to think, based on the tests, which I think they believed in, that they were equal, but perhaps it helped his ego to know he had that one point edge on paper. They used to joke about it. You do the taxes, you've got that extra IQ point.