here is a little working list of salary paying US firms (pretty much all options market makers)
Spot Trading (prop trading pays a salary, upstairs)
Jump Trading (prop trading pays a salary, upstairs)
Infinium Capital (CBOE equity, index, CME financial & ag, on floor & upstairs)
Wolverine (CBOE equity & index market making, CME, on floor & upstairs)
Group One (CBOE equity market making, on floor)
Jane Street Capital (does equity market making as well as pairs trades / they allege "stat arb" wrongly, on floor & upstairs)
Ronin (market making w/ some prop mixed in I think, not positive they start you on a salary that but I believe so, on floor & upstairs)
Belvedere (SPX, OEX market making, on floor)
Transmarket (CME fixed income market making, upstairs)
Susquehanna (CBOE equity market making, ETF market making, on floor & upstairs)
IMC (CBOE equity & index market making on floor & upstairs)
Optiver (CBOE equity & index market making all upstairs)
Peak6 (CBOE equity market making all upstairs)
Chicago Trading Co. (CBOE & CME equity & index market making on floor & upstairs)
Liquid Capital (US & UK, in US, CBOE & CME index market making on floor & upstairs)
Blue Capital (CBOE SPX, RUT, OEX market making on floor, some upstairs prop, not sure if they are hiring new guys)
KC Co II (CME index market making on floor & upstairs, again not sure they are hiring new guys)
Everest (CBOE equity mm on floor, no web-site that I know of)
Knight Capital (don't know how many are sales-traders v. market makers, upstairs)
Bear Wagner (NYSE specialist)
Oscar Gruss & Son (same)
GFI (again sales trading mostly, but know some guys do executions, upstairs)
First New York (prop gig no MM, but pays a salary, upstairs)