There are many different options, and which one(s) might work is highly dependent on the situation, the information needed, and the people involved. For the purposes of this answer, I'm going to refer to your colleague who hasn't responded yet as Jamie.
If you're located in the same place as Jamie, a quick hallway conversation is a potential method to address this. When you run into Jamie in the hallway (and this can include manufacturing a way to run into Jamie in the hallway; I've found inobtrusive ways to hang around somewhere where I knew I would eventually find Jamie), you can just ask your question again. When I do this, I generally don't reference the prior email at all (although I will acknowledge that I sent them an email if they mention it), I just ask my question. The less-casual version of this is stopping by Jamie's office/cube/desk/whatever.
If you're not located in the same place as Jamie, then try other non-email contacts to see if they work: phone, instant message, etc. I'll admit that I dislike the phone and so very very rarely call someone if I need information from them.
If you don't know Jamie very well, you could ask trusted colleagues if they know of a good way to get a response from Jamie. You might learn that Jamie just is not very good at responding to email but is highly responsive if you send an instant message. Or you might learn that Jamie is usually awesome about responding to mail, but tends to go silent on email when they're in the middle of a big thorny problem, so you'll need to resend your mail when that big thorny problem has resolved itself. You might also learn that someone else can answer your question, which resolves the actual issue (that is, getting the information you need).
If you're stuck with email for one reason or another, then you could respond to your original email to Jamie. When I do this, I tend to say, "Jamie, have you had a chance to answer this yet?" If it's blocking me on completing another task, or if I've asked because my manager has asked me this question, I'll add something to that effect: "I need this so that I can be prepared for the meeting on Tuesday." You can also ask Jamie if there is someone else who might be able to answer your question instead.
If you just need the information, and if your company is one where meetings are part of the corporate culture, you could schedule a quick 30m meeting with Jamie to get the information that you need. This is especially useful if the information that you need is detailed or nuanced. If I do this, I take notes during the meeting, and I send them to Jamie afterwards to ensure that I've captured everything that we needed. Also, if appropriate, I post my notes somewhere internal, so that anyone else who needs this information can find it without having to resort to scheduling a meeting with the one person who knows.
If you've tried to get this information from Jamie multiple times, and if Jamie really is the only person who knows this information, then I'd respond to my email chain again, this time CCing my manager. Depending on the organization, CCing a manager is an excellent way to get a response. If your organization is one where doing this will get a response, use this carefully and sparingly -- Jamie could perceive that you're trying to get them in trouble, and that's never good for building relationships and getting information in the future.