You might be surprised by how much innovation there is in the seemingly simple world of highlighters. It still surprises us, and we're a pen shop, so we should be used to this sort of thing by now. Everyone knows about the classic Stabilo Boss highlighter, but did you know they are refillable? Did you know there's an executive version of the Boss, with rubber grips, and a different ink that's less prone to smudging inkjet print and fountain pen ink?
Other interesting innovations in highlighting technology?
Dry highlighters are a bit of a different solution to the problem - essentially highlighting pencils, with bright neon lead - great if you tend to leave the lids off your highlighters.
The Kokuyo Beetle tip highlighter can highlight in three different ways from one highlighter in the shape of a 'normal' pen. Fine, broad or even double-lined.
The Uni Promark View solves a problem you may not have thought about at all - the highlighter getting in the way of what you're highlighting! Ever drifted off the line you're trying to highlight because you can't see what you're doing? Or not known when to stop until you've gone a bit past the end? The Promark View's clear tip lets you see through so you stay on track.