Love the E46, and while it's not insanely high HP, BMW straight 6s are just fantastic, just generally awesome driving dynamics.
$25K? Yeah, a Focus ST would be fun, they're super little sport hatches, easy to tune for more power, the RS is fantastic, but I think finding one for $25K might be tough (unless it was just beat to hell).
Pure fun factor, a little 2-seat roadster is always a blast, I always found Miatas just a tad too small/underpowered, but I had an S2000, which is pretty fantastic and still looks incredible modern (they really knocked it out of the park with that design) - or maybe a Z3 or Z4, you might also look around for an Z/M Coupe, the hardtop Z very cool, rare.
A Mustang GT in that price range would be pretty capable, get a Perf Pack car, there's so much aftermarket (if you're into that) performance, handling, etc. The WRX you mentioned is fun, lots of capability.
I guess one of the things would be if you wanted to really change up the whole experience, like I went from a Z06 so an S2000, talk about a change