Essential NRaas mods in my game (several of these are due to my tendency to play overstuffed households): Overwatch, ErrorTrap, Traveler, MasterController (with Cheats, Integration, ExpandedTattoo modules), Mover, Portrait Panel, Register Relativity, Retuner, Saver, Traffic. I also really like StoryProgression and Careers (with PartTime, Schools, SelfEmployed, Tones, and Unemployed modules) and Tempest.
Other essential mods: Add Any Lot Size, More Entry Points, Same Energy for Every Bed, icarus_allsort's call to meal mod (mainly because it tells me how many leftovers are available).
I get a lot of residential houses from http://www.mysimrealty.com/