Get something waterproof, breathable, and most importantly, wind proof. If you can wear them both as over pants or as wear alones, they could be more versatile.
Aerostich AD-1's, Darian pants, or Darian Lights...pretty pricey stuff, and probably your benchmarks.
My Triumph 5-pocket textile jeans have really proofed their worth over the years, though. Kind of a stretchy black cordura, Jean-style (but I really like the little coin pocket on the left side!), with a wind proof, water proof membrane sewn in, and fully lined with nylon flat mesh...dressy enough (black enough) to get away with that, too, on occasion.
I think I gave $100 for them, probably back around 2005. The waist hook loop pulled through the cordura, and the cordura around the hole the hook pulled through was tough enough to hold them up for a year or two, and then I had the bootmaker sew in a big snap reinforcing the area in leather.
Triumph makes several versatile riding jeans and pants now, and I like their stuff. Never complained about anything I bought to wear that Triumph sold.
