So, I'm gonna pop up a few resources for the Planescape game(s) - system neutral, of course, so I can use them either way (though I might add some stuff for Risus/FATE where appropriate).
First up, a classic location - the pub.
The Laughing Paladin Inn
Named after Shair Kress, a planar Knight of the Silver Flame, who famously stood before a Pit Fiend and laughed at its great boasts of martial prowess (before being soundly defeated and eaten), The Laughing Paladin is a pretty decent place to be. A decent looking building (think an old Victorian public house/inn, with some Sigilite trappings, and you're there), it bears the crest of The Silver Flame as its sign - making it a first stop for any planar adventurers from the land of Eberron. Most of the clientele are of a Lawful bent, and run the gamut of races and species present in Sigil and the Planes beyond. Rooms are varied - a few copper nets you a decent room, and 20 will net you a nice one. Drinks are pretty nice - nothing Lower Planes-related on sale here, mainly Prime ales and spirits, and the odd Ysgardian brew. The food is... not their strong point, but certainly passable. Occasionally, groups of Harmonium namers will happen by the place, to find out the word on the street about other factions, goings on etc. Those who are looking to dodge the Law would be advised to stay clear.
Rose-That-Grows-On-High Sharri Vass is the barmaid, part-owner, and security, all rolled into one. A Goliath, she has some hint of Stone Giant or other Earth-Elemental creature far back in her lineage - attested to by her height (7' and a bit), her physique (go check out a toned female bodybuilder, but not one of the huge super-muscled ones), and her lithoderms (little stony growths covering her skin at regular intervals). Even though she is creeping into middle age, her imposing physique ensures no-one thinks to take advantage of her generosity.
Rose was, in fact, a travelling companion (and some say lover) of Shair Kress, and opened up the pub in his honour. Chant is, Rose gets the itch to go adventuring every now and then - become a regular, and catch her in the right mood with the right tale, and you could have a powerful ally on your side.
Notes: use Aspects and Stunts/Cliches and Funky Dice to make Rose strong. Depending on your campaign, this could be anything from "as strong as a 7' bodybuilder should be" to full-on Giant Strength, hurling boulders (and enemies) like cardboard boxes. A little competitive and hotheaded, and very useful in a fight. Rose should remain as a "back-up" character when all else fails - she has the pub to look after, remember?
Varren (last name unknown) is the Tiefling chef, working most hours of the day in the kitchen of the Laughing Paladin. At night, he is known to prowl the Hive Ward, hunting for Clueless and other sods with more money than sense, and helping them out with balancing the two. Those in need of a less than reputable contact, a stealthy ally (technically, a stealthy merc) or someone with connections to the Lower Planes would do well to see him.
Notes: Varren keeps himself to himself, mostly. He will work for you, but you'd better be paying him well, and keep an eye on your valuables. Rose knows that he's a bit evil, but she hopes the influence of The Laughing Paladin will help him turn to good. Fat chance. Varren is actually statted out for Risus in my Planning post - go find him!
If you do end up taking Rose with you, a good hook to use when you return would be that Varren has taken the place over - and made it a little home away from home for the various Fiends that frequent Sigil. Have it look real bad - arm-wrestling baatezu, Succubus strippers, dead-thing decorations, Neogi slave auctions, the works.
You need to help Rose restore the Laughing Paladin to its former glory - but Varren has something on his side you cannot hope to match - lawyers. The best deal-making, contract writing Devils around frequent the new bar, and they're not letting go without a battle. A legal battle.
As many adventurers from Eberron will flock here, you might find people hiring for explorations of the jungles of Xen'Drik, or recruiting for other adventures back home - this can make for a nice diversion, and the chance for some Prime-based adventures (something that makes a nice change from continual Plane-hopping, and gives a good excuse to get players from Eberron to Sigil).