any websites devoted to classic sega games?

arcade, master system, genesis, saturn, gamegear, dreamcast you name it

descriptions, reviews, hints and cheats??

I'm guessing you're looking for general SEGA sites

Sega-16 - is a decent site, covers the whole Mega Drive plus other stuff, great info on Arcade boards and some good articles

SMS power - Master System site

SMS tribute - another Master System site

Segagaga Domain - huge database of a single guy

Segafans - kind of dead site

I know of other English sites, but I can't recall the links, also know some French and Japanese sites, but I don't know if they'd be of any use to you.

The best SEGA sites are from gaming specific sites though, like the Shining Force Central or The Will of the Ancients.

There is a union here atGameSpotAll Things Sega Union
I'm sure there are more.
I'm bet if you ask in their forum they can hook you up with more.

Google is your friend
I found this one right away that lists a few sites for each platform.
http://www.segaoa.com/

I see Panzer_Zwei already listed some of the others I spoted 8)