Usually half the fun is in painting your army, and ebay seems to sell mostly pre-painted models. You'd have to make sure the army books are the most recent versions too, unless you're looking for the older ones which have more fluff (but aren't compatible with the current rules).
Quick presentation: Games Workshop has two main games, Warhammer (also called Warhammer: Fantasy Battles, or WFB) and Warhammer 40.000 (often shortened to WH40K or even 40K).
- The world of Warhammer is one of fantasy, with elves (high, dark, wood), orcs, humans (Imperials, Bretonnians), dwarfs (regular, Chaos), skaven (Ratty's kin), lizardmen, chaos warriors, chaos demons, and chaos goatmen. Armies are made of regiments (minimum 5 or 10 models) organised in close ranks, with artillery, monsters, and heroes for extra punch. The various races are described in Army Books.
- The world of Warhammer 40.000 is a sci-fi one, with space marines (the most popular because they're tough and easy to paint), orks, humans (Imperial guard), Eldars (=elves), Dark Eldars, Chaos marines, Sisters of Battle (power-armoured nuns), and tyranids (think Aliens). Armies are made of squads whose members must be 2 inches from each other, with vehicles and heroes for extra punch. The various races are described in Codexes (calling them Army Books will get you a rough time in France). Troops are more mobile than in WFB, and there are obviously more ranged weapons.
A battle lasts for 4 to 7 turns made of separate phases : movement / magic (WFB) / shooting / melee / rally. Each player has a whole turn in turn (if you see what I mean). Points are awarded for destroying units or for mission-specific objectives. Games can last upwards from an hour.
Other GW games include :
- Mordheim (WFB universe), Necromunda and Gorkamorka (WH40K universe), where each player controls a gang whose members gain experience and equipment between battles. Rules are more detailed, and include weapon jams and knock-outs.
- Battlefleet Gothic (WH40K), where each player controls spaceships.
- Warmaster (WFB) and Epic 40.000 (WH40K), where each player fields an huge army of tiny models (about 1/4 the size of WFB models).
- Blood Bowl (WFB), American football with weapons.
Phew! Any questions?