You can always make do with the stalk mic sticking out of your gaming headset, but there are very few that can come close to matching the recording quality of even the cheapest gaming mic on this list. If you're planning on streaming or recording your gaming, and what to add your own voice to the mix, then making yourself sound better than your weedy headset microphone is surely a must.
Having a good mic will also mean you don't have to use a gaming headset at all. For us audiophiles who prefer a great set of headphones that come without a mic at all, a desk-based option is the only way to roll.