Well, off the bat, Bicals are pretty much the largest and fastest growing nepenthes that you can find. Also, if you haven't grown any before I'd suggest not starting with seed, since it will take years before you have even a small specimen. Order from one of the few great vendors that are online. I can PM you a list if you don't know who they are. There are a few fun ones that will stay small-ish for a while, but nepenthes are vines and will eventually outgrow a 29 gal tank no matter what.
Edit* I just saw your very beautiful and large ampullaria in the other thread, so I guess you obviously know how big plants can get. As was said above, belii would be your best bet for a small LLer, although even belii will get big over time. Theres one here at the huntington gardens thats easily a 4-5 foot vine with a few rosettes that are over two feet wide. Pretty much, there is no such thing as a nepenthes that will fit inside a terrarium forever. If you wanted to grow highlanders, there are a few plants like aristo and gymniphora that will stay pretty small, but will still grow a long vine like any other plant eventually.