Are you getting enough support and help with the new baby? Mommy's health and happiness are vital to babies and childrens' growth and development. Maybe have your hubby take over the whole nighttime routine (bath, brush teeth, book, bed). Or if you can, find a friend or family member to take your son to the park during the day, or take the baby for a while. You need a little time to yourself right now every day (as crazy and impossible as this may seem).
Co-ops and moms' groups could also be the ticket for letting off toddler energy. Maybe putting both in a stroller/carseat and going for a walk/drive can give you the time you need to regroup your sanity. If mommy is frazzled at the end of the day, the child might be picking up on this this energy at bedtime.
It does seem that with the timing your son might be more clingy because of the new sibling. I have read that now is the most important time to be there for him and let him regress a little, so that he knows he is still safe and secure and loved. It might also make him less jealous of the new sibling.
Having said all that, my 24 month old son also takes a long time to go to bed. Here are some general things that have helped us and may or may not be applicable in your situation (I am due in November so I have yet to experience the double duty you are going through!)
1. Taking a 2 to 2-1/2 hour nap in the afternoon. This may sound counterintuitive, but the better he naps in the day, the better he sleeps at night (fewer wake ups, faster falling asleep). Keep the room dark and quiet, or use a fan for white noise, to help him sleep longer.
2. Wearing him out in the day -- both physically and mentally. A lot of stimulation and a lot of exercise (this is not always easy or possible to do - being around other people helps) he'll usually go to sleep earlier and more quickly.
3. Having enough one-on-one mommy/daddy time. Sometimes he'll want to stay up longer because I have been too busy for him during the day and not really interacted with him enough. Sometimes he really wants to spend more time with daddy before he goes to bed.
4. Sometimes he is hungry, believe it or not! If he hasn't eaten well in the day, feeding him at bedtime often works wonders to put our son to bed. Either way, I always give him bottle of warm milk (tryptophan induces sleepiness, and warmth too) before he goes to bed. Add fruit, yoghurt or a full-on meal depending on his hunger level.
5. Ambience: dim lights, soft music, calming bedtime books and soft voices make a huge difference with us. You could also try a dimmer light or a bright night light.
6. When all else fails, sometimes (when desperate) my hubby will put him in the carseat and drive him to sleep -- this works esp. well when he is clearly sleepy to begin with.
Mostly, we just accept that it takes a long time for him to go to bed and try not to be too hard on ourselves (they are, after all, only human and not trained robots). I have heard that this time of transition is the toughest part but it gets easier with time. Hang in there -- I just hope I will have the energy and strength to get through it myself!