The current non-BB engines are typically in the .6 hp range. Thunder tiger GP25 and OS 25 LA are good choices for this class. For a little more money, and weight, you can get one of the BB engines. They are typically .8 hp or better. Examples include Magnum XL-25A, GMS .25 BB ABC, and OS .25 FX.

If you're looking at older engines on eBay, my all time favorite 25s are the OS .25 FSR and the 25F ABC. I've got one of each, that I bought new in the '80s. I flew the 25F in a Modeltech Extra 300 ARF all summer. Not a single deadstick. The FSR does not have as much power, .6 hp versus .8 hp. Amazing how little progress has been made relative to hp, eh?