Depending on what else you need the router to be able to do, pretty much all Cisco routers support 802.1Q subinterfaces.
You said a medium organisation though, so I'd say any of the 2800-series (2801, 2811, 2821, 2851), or at most, the 3825. Which one you choose depends how much traffic you expect this router to experience, and what other features you require.
It also won't matter what IOS feature set you use, unless you have a specific requirement (VPN, VoIP, etc), as 802.1Q is supported in IP Base images.
Hope this helps!