I just read through the twilight books for the second time and I am feeling the exact same way. (but too embarassed to admit it to my friends... eek, Hi my name is Wendy and I love a teenage romance vampire book - who am I??)
But!!! I can second the suggestions for the Outlander series, except I would suggest quitting them after Drums of Autumn... I know, blasphemy - but I just couldn't get through the one after that, or the one after that one..
I also second Time Travelers Wife - I too just saw the preview for that one and it brought back all the lovey feelings I got from reading it... god, that was the best book! I am thinking I will pick that one up again.
I did really love all the Ann Rice vampire books back in the day - those were good. They sweep you up in this world and its hard to come down out of it. I also loved her Mayfair witches series... what was that called? I can't remember - but I remember being totally in love with it.