Creator Cameo: One of the show's writers, Wendy Molyneux, voices Jen the babysitter.
Cross-Dressing Voices: Linda's and Tina's voices are provided by John Roberts and Dan Mintz, respectively.
For that matter, most of the one-shot/background female characters seem to be played by men, too.
And then you have the Pesto twins being voiced by Sarah Silverman and her sister, Laura.
Hey, It's That Voice!: 95% of the main cast and the guest voices are people known from the sketch and stand-up comedy world. The other 5% are from other TV shows, particularly those that are either considered modern cult classics or earned the title of being a cult classic because the show/movie was either screwed over or caters to a nerdy, pseudo-mainstream sensibility.
Bob is Archer and Coach McGuirk. The first episode of Archer's fourth season even had an amnesiac Archer think he's Bob Belcher and had the Belcher family drawn Archer-style.
Tammy the bad girl is Jenny Slate, a one-time Saturday Night Live cast member who got in trouble for accidentally saying "fuckin'" during "Biker Chick Chat," her very first sketch on the season 35 premiere hosted by Megan Fox. Slate is also the voice behind "Marcel the Shell With Shoes On", was on an episode of Raising Hope as a social worker, and was Stella on the short-lived noir parody Bored to Death.
The gay butcher from "Turkey in a Can" is Bob Hunter.
What Could Have Been: In the original pitch of the show, Bob and his family were cannibals who served ground-up human meat to unwitting customers, while trying to keep the authorities off their trail. Naturally, something that disgusting got rejected as a series premise for network TV (it'd be a different story if it were on cable — either basic or pay-premium), but it didn't stop the first episode from alluding to it.
Tina was also supposed to be a boy named Daniel.
John Roberts originally auditioned to be a cast member for Saturday Night Live during the 2008-2009 season (when Amy Poehler left to have her baby and do other projects, so Lorne hired Bobby Moynihan, Abby Elliott, and Michaela Watkins). Had he been chosen, not only would John Roberts be the second male homosexual cast member (and the first one hired since 1985), but he wouldn't have been the voice for Linda.