I'm glad you asked! I've been on a rampage collecting such quintets for IMSLP. Here is the complete list (disregard the self-published educational stuff from IMSLP users):
Category:For violin, viola, cello, double bass, piano - IMSLP: Free Sheet Music PDF Download
The Vaughan Williams is my favorite so I'm glad you're already aware of it. After it and the trout, I really like Cramer's third quintet, which was recently published by Kammermusikverlag. It's amical like the trout, although the piano is a little bit more heavy-handed, but the bass part was written with Dragonetti in mind so it sounds like a lot of fun. Here's the
sheet music and
a recording. His first and second quintets have the same instrumentation and are on IMSLP in the form of parts with no score and have not been recorded.
From neilG's suggestions, I like Labor and Goetz the best. Labor is a very imaginative late romantic work written for Franz Simandl with a totally independent bass part; in fact, all five players have equal independence and solo time. Goetz is dramatic without being orchestral and the andante is absolutely wonderful, with all five players weaving in and out of the texture, with some occasional limelight for the bass. However, the first movement is very desolate and may tax the listener's patience.
The Limmer, Dussek and Hummel are mini-piano concertos which is not my cup of tea. The Onslow fits this category as well (he has one quintet originally written for this group and two others that are arrangements of his own pieces). There is another French contemporary of Onslow's, Adolphe Blanc, with a piano quintet that has not been recorded. His style is much more elegant and chamber-y than Onslow's although he writes less interesting bass parts:
Piano Quintet, Op.39 (Blanc, Adolphe) - IMSLP: Free Sheet Music PDF Download
I also want to mention Louise Farrenc's two quintets which made her famous, and they are excellent, but held back by an overreliance on piano pyrotechnics.
There are two more quintets which I've unearthed recently which have not been looked into yet, by Reissiger and Sowinski. They also strike me as intimate in the vein of the Trout and may be worth trying out:
Piano Quintet No.3, Op.209 (Reissiger, Carl Gottlieb) - IMSLP: Free Sheet Music PDF Download
Piano Quintet, Op.87 (Sowinski, Albert) - IMSLP: Free Sheet Music PDF Download
And this isn't even half of what is out here. Possibilities abound, including some modern premieres.
