Gmail has released a new labs add-on (the fifth this month) that tweaks the service's search tool, providing suggestions for contacts and search modifiers as you type. This means that when searching for messages from a specific person it will automatically begin to provide suggestions of who you're trying to search for, just like it does when you're composing a new message.
What's nice is that this same system also works for remembering any of Gmail's search operators, so you can do things like type in what date range the message should be from, what kind of media an attachment should be (like videos, pictures, or zipped files), or simply look up things by file name. All the while it sticks the modifier in there for you, and without you having to remember the proper nomenclature or where to stick the semicolons and parenthesis.
While you could get many of these options just from using Gmail's advanced search tool, I like this add-on because it puts everything in main search bar, which sticks with you no matter what you're doing on the service. You can find it near the bottom of the Gmail labs add-on page.