As a healer, HealBot (I know others say VuhDo but I sed HealBot first and just got used to it.
For anything else...I don't know...maybe Z-Perl Unit Frames? not very particular, I just don't like the default frames, and Z-Perl is practically good to go right out of the box.
Also, WoW-Pro for leveling, gives the most efficient routes and quest order to level the fastest.