Villas are roughly grouped around three main areas - US27, Formosa Gardens and Poinciana Blvd.
The US27 intersects with the extreme west of US192 (the main tourist corridor in Kissimmee). There are a few villa communities heading north on the 27 and
lots heading south.
The Formosa Gardens area, west 192 near marker 5, has a high concentration of sub-divisions located immediately south of WDW property at its most westerly corner. These communities are the closest to Disney and it's possible to be in the parking lot of Animal Kingdom within 5-10 minutes using the Sherberth Road. Due south of the FG area are several other communities including ChampionsGate and Reunion. Don't write these off as, although they're further away, they're right next to exit 58 of the I-4 which makes for a very easy hop to WDW, UO and SW.
Poinciana Blvd is a rural stretch which runs south from the 192 east of Disney. Where the two roads intersect, you just need to hop across the 192 and onto the Osceola Parkway for a quick and easy drive onto WDW property. Obviously the closer you are to the 192, the quicker your journey. Cumbrian Lakes, which Kenny mentions and where we've also stayed, is about 4 miles south of the 192. BellaVida, where Tracey has stayed, is around 2 miles south. Any of the communities north of the US17/92 is fine, but I wouldn't advise straying into territory south of that.
This map gives a good overview of the area's rental communities.
This interactive map, whilst a little out of date, shows the communities in greater detail. Click first on the links to the individual maps, then follow the links to villas (click the ones which say "map" rather than the ones which say "book"). You'll then find a list of sub-divisions in that area. Clicking on the name of a community will take you to a map which shows where it is in relation to the others.
In addition to those already mentioned by Kenny, I like
this site for scouting out the options.