The road heads East a short ways before you encounter a trainer, just as the route zig-zags to the South and then East again.

Battle: Depot Agent Hank (1000 Poke)
Opponent: Drilbur Lv 25

Going a bit east will likely run you into the next trainer directly- a biker.

Battle: Cyclist Hector (800 Poke)
Opponent: Tranquill Lv 25

A diversion to the North of the paved road holds some grass where you can catch a few things at levels 21-24.  Liepard are here, as are three new opportunities. 

Minccino is an often-underestimated cuddly-looking Normal-type that becomes the quick but frail physical attacker Minccino, who can really abuse a few of the stronger Normal attacks, particularly if equipped with a Silk Scarf and the Technician abilitiy (Tail Slap, I’m looking at you).  Trubbish is a Poison type in the same mold (ahaha) as Grimer and Koffing, with Garbodor having a similar mediocre speed, somewhat less powerful defenses than its predecessors, and a small leg up on them in Attack.  Its abilities are also a bit odd, but with some planning it can be very usable. 

Black 2 players will be able to get ahold of Gothita, whose final form, Gothitelle, is a rare slow, highly defensive Psychic type- but sadly lacks any other way to distinguish itself.  Usable, but not great.  White 2 offers Solosis, whose final form, Reuniclus, is a rare slow (even slower), highly defensive Psychic type (albeit with much more HP and somewhat less defenses) with a monstrous Special Attack and the movepool to abuse it.  Trick Room’s effect is horrifying when combined with Reuniclus, so it’s just as well that it can’t get its pseudopods on that move itself.  It still packs a lot of tricks and powerful attacks, though.