What would cause my 2005 Honda Accord to "shake" at 25, 35,45 mph?

This could be caused by numerous things. Check your suspension, Stabilizer links and ball joints are a common issues for vehicles. I'd look at these first. While your checking these check control arms and wheel bearings next. Warped rotors can also give you a shake.

Good morning Stanford. But grkilgore_va are you sure it's not wheel balance when you say 'not tires'? Do you feel it in the steering wheel?

Have you had any work done on the vehicle recently ? May be loose lug nuts.

Tires would be number 1 reason, leaky bad struts, loose lug nuts, bent wheel, bad wheel bearing, bad cv joint, loose suspension parts,engine miss etc.

Good afternoon Fordnut.

Good Afternoon Stanford.....

Could also be the torque converter not operating properly, but hard to tell with your description of what's happening.

Whats up Bob!...being helpful as always I see.