i would also suggest trying some more powerful racquets and possibly order a roll of lead tape too to try adding more weight to them.
yonex makes an interesting range of racquets... even there more powerful racquets tend to feel more head light and lower swing weight than their competitors. try a Yonex vcore 98 or maybe even vcore 95D?
as TW racquet guru Chris mentioned, try a babolat pure drive or clone (head instinct, wilson pro open, etc) unmodded and see how it goes. if too whippy and powerful, and add 10grams to the tip of the racquet. try serving with that... if still no good, try counterbalancing on the handle too.
if those racquets are just too powerful or still don't help with your serve, i also find the head IG Speed to be an interesting frame. has the thin beam of a prestige, swings through the air amazingly quick, and has a mix of control and power. i also recommend trying lead on this racquet. it has such a low swingweight that you can really add a lot and still be able to swing it. adding some lead in the hoop and throat will definitely give it more plow if needed.
there are a million things to try, which is fortunate or agonizing depending on your point of view. if lighter but thin beamed doesn't work... you could try larger head and lighter but very flexy like the Blade 104 or Radical OS.
of course, taking some tennis lessons for some review of your technique might be the best thing to see what they could suggest for your serve with the racquet you like best on other shots... or practice your michael chang underhand serve! they can be deadly with the right spin!