My updated set of recommendations:

1. Optifine - allows you to tweak display settings and certain game elements giving excellent game performance even on 32 - bit systems.
http://www.minecraftforum.net/topic/...and-much-more/
2. Custom NPC's mod - create your own NPC characters in Minecraft.
Fully customizable, meaning you decide everything: type, size, skins {compatible with most skins made for 'Human Male', like Steve, so you can use skins people upload to PMC and other sites}, assign jobs, factions, etc, etc.
All this and it adds numerous items such as weapons, armor, food, quest items, and more.
http://www.minecraftforum.net/topic/...-npcs-splanmp/
3. MACE city generator mod - a standalone program which generates worlds with cities. {NOT just random like it says, they're fully customizable with dozens of city options - why do they say random when it isn't?}.
There are 3 basic themes {desert, medieval, and Novv - sort of medieval with lots of detail} and you can insert 1 - 100 cities of your choosing into generated worlds.
Name the world or leave MACE to give it a random name, insert a world seed, tweak the options to make them contain only what you want them to, then create a profile so you can duplicate your favorite cities again later!
http://www.minecraftforum.net/topic/...ies-generator/
4. Tale of Kingdoms mod - I consider this to be part mod, part city generator; the mod inserts a medieval style building {into either a new world or an existing save file}called the Guild.
The Guild is the starting point of the RPG aspect of the mod.
NPC's in the Guild inform you that you are the King who must complete certain tasks in order to gain the trust of your people.

Once you gain their trust {by gaining enough in - mod 'EXP', basically} you can then choose the site of your Kingdom, which you provide the raw materials to build.
There are 3 tiers to the Kingdom, expandable as soon as materials become available.

IN CONCLUSION:

These mods used together hold HUGE potential both on or offline and the best part is that you can do what I did:

Use MACE to create a world with a city {or cities}, then install the TOK mod, play to gain the Kingdom, and then uninstall TOK and use the Custom NPC's mod to make your own characters, storyline, whatever!

And in case you were wondering it is possible to have both mods running at the same time, but your custom characters better be tough enough to stand up to the TOK hostile mobs!