<input type="submit" value="Search"> is fine and is the most common solution. But <button>Search</button> is also completely fine, and if you want anything other than plain text as a button label (e.g. images, variable formatting), it’s the approach you have to use. (When used in a form, there’s an implied type="submit" on it. With type="button" it would lose the submitting functionality and become obviously unsuitable.)