The Sega Megadrive (Genesis in the U.S) was launched in 1989, the MK1 model has an AV socket for scart, an RF socket, and a  headphone jack with a volume control slider on the left hand side (you can only hear stereo through headphones unless you buy a special cable). It also has "16 bit" in raised gold letters on the front, and a grey "reset" button.
The later Megadrive\Genesis (mid nineties) was completely redesigned, the RF socket is done away with, so you are left with just an AV socket to connect (smaller than the Megadrive AV) the machine it's self is smaller, with red "reset" and "power" buttons, the headphone jack was also removed and full stereo is avaliable through the T.V.
Choosing which model to buy is down to personal preferance, they can be bought for around £15-£20 and most are reliable and robust.

Cartridge Compatibility & Converters :
In most cases the only limiting factor is the shape of the cartridge, most U.K and U.S cartridges are the same shape and play fine in any machine, but Japanese cartridges require a larger cartridge slot or a converter. Most converters are straight through connector devices, but if a cartridge has "region protection" built in (notably later Capcom and Konami games) you will need a converter with "dip switches" on it to bypass the protection. 

Cleaning Cartridges :                                                                                                                      

First of all you shouldn't blow into your cartridge, it will do nothing to remove the build up of 17 years worth of crud.  You can clean your cartridge safely with some "Cotton Buds", a "Toothbrush" and some "Isopropyl"  or "electrical Contact Cleaner" if you have some, (often found in video head cleaning kits) you don't NEED Isopropyl or Contact Cleaner, but if you have some, two drops on the cotton bud should be sufficient enough, JUST to dampen it. Now you can rub on the gold pins of the cartridge until there is no more black muck left on the bud.  Finally you should rub with a dry bud to absorb any moisture left over, and brush out any snagged cotton with the toothbrush, leave the cartridge out for a while if you used Isopropyl, as a just in case measure to allow any moisture to evaporate.   

Top Games :

Too Many to List Here, so here is a rough guide.

Any Capcom Title ( Street fighter etc.)  Any Hudson Title ( Mega Bomberman etc.)  Any Disney Title ( Castle Of Illusion etc.)  Any Treasure Title ( Gunstar Heroes etc. )  Any Sonic Title ( Sonic 2 etc. )  Any Shinobi Title ( Shadow Dancer etc. )  Any Streets Of Rage Title ( Bare Knuckle in Japan )                                                                                               

Worst Games :
Any sports title (look to Next Gen consoles for sports)
Any Menacer title (Light Gun Games)
Any Racing title (Monaco GP and Micro Machines excepted)
Muhammad Ali Boxing (UURGH!)
Ultraman

(see my Megadrive games reviews)

Peripherals and add ons :

Arcade Stick I & II
Awesome!!! heavy and robust, a must have for any serious gamer.

Menacer Light Gun
In a word .... Shite! Ugly, clumsy, awkward and not many titles supported.
 
Mega CD & Mega CD II (Sega CD in the U.S)
The Mega CD 1 was a handsome beast, it sits underneath the Megadrive, and has a classy front loading CD tray.  The Mega CD II was designed to sit side by side with the Megadrive II, it has a top loading door for CD's, and it has to be said looks cheap and plasticky in comparison.  A large library of titles were released for the system, mostly rubbish FMV games, and a few straight Megadrive ports which are exactly the same, but with CD sound, although there are a handful of gems. Mega CD II can connect with Megadrive 1 with out problems.

32X
Only 30 odd titles released for it, so it is possible to collect all of them, although prices are stupidly high for some games (£200+), considering that there are only a few worth having. The system had a short life due to the imminent release of the Saturn. The 32X looks awkward, perched on top of the Megadrive like a bad Ascot hat, it requires it's own power supply and link cables, and quite frankly doesnt live up to its "32 bit" hype. (see my 32X games review)

Master system Convertor I & II
Does just what it says, allows you to play Master System games on your Megadrive, be wary though, the Master System Convertor II doesn't have a slot for sega card games.

Summary :                                                                                                                                                                                                                                                                                                                                                        All in all the Megadrive is a good machine with a massive library of games to choose from, just dont expect it to compete with Playstations and Dreamcasts (or Super Nintendo for that matter). As a retro machine though, it triumphs, it will take you back to a mis-spent youth, a time when 16 bit was king, and a golden age of gaming was being born. 

PS  Please note that this is JUST a guide based on my personal knowlege, and NOT an F.A.Q. or bible, so if you think I have missed anything, or have any questions that relate to this guide, please feel free to e-mail me through ebay, I will be happy to update the guide accordingly.

If you found my guide helpful please vote by clicking the button below. Cheers, Paul.