It depends on what you are wanting to do with it tbh, but there are a few general things i'd recommend:
1: Some sort of Flash blocking app or browser extension (it will improve battery life if you browse the web alot)
2: VLC Player or Perian Quicktime plug in for movies.
3: If you havent already done so buy an external hard drive and configure Time Machine for backups.
4: If you are unsure of a good word processor and your needs are basic i'd try Pages, it's only £7 from the App Store. Its not free like some alternatives, but its cheap as chips, easy to use and is well integrated with Lion.
Hope some of that is helpful, but i found half the fun is figuring out exactly what works best for you. enjoy your new purchase and have fun getting it all just right! 🙂