You should check these out:
A septet for trumpet, piano, string quartet, and bass, along with some other delightful chamber works:

Six discs of quintets, sextets, septets, octets, and nonets with well-varied instrumentation by early Romantics:

Bax wrote a number of chamber works for unusual ensembles, such as an Elegiac Trio for harp, viola, and flute and a Fantasy Sonata for harp and viola:

most obvious: Schubert's "Trout" Quintet that needs a double bass
There's an excellent period group, the Nepomuk Fortepiano Quintet, that's recorded three albums on Brilliant of works for that supposedly unusual ensemble:

So far, they've covered Hummel, Dussek, Onslow, Ries, Limmer, Cramer, and Schubert. And CPO has released an excellent disc of two piano quintets with bass by Louise Farrenc, one of the great unsung Romantic female composers.
Onslow's various sextets, septets, nonets, etc. feature a varied array of instrumentation:

Didn't someone recently mention a string quartet with two cellos? I regret to say that I have forgotten whose work it was or who mentioned it.
Boccherini wrote numerous string quintets scored for two cellos (and three for string quartet plus bass). I don't know about quartets with two cellos, though.