Look for Swiss-water decaf black or green teas; stay far far away from the standard solvent extracted teas - not a very healthy alternative.
Oolongs have about 1/3 lower caffeine, but still may be enough to keep you awake at night if you're caffeine sensitive.
Herbal teas can range in flavor from grassy/vegetal to bland, tart or sweet. You'll have to experiment. I would start with our host's herbal blends and decafs, particularly the decaf spiced green and earl grey teas. Haven't tried the decaf ceylon, although it's been positively reviewed. I would try it as a base for blending in a bit of fruit or flower flavoring if you're desiring a complex after-dinner tea.
Another alternative is to brew Kukicha Twig Tea, which is naturally low in caffeine and requires a longer steeping time (up to 10 min).
I can also recommend the decaf Darjeeling tea from SpecialTeas, also the English Breakfast decaf. I'm not a fan of decaf teas because the are usually very bland compared to the caffeinated versions, but these are quite decent for decaf teas.
I've heard their decaf sencha is also passably drinkable, but haven't tried it myself.
I find roiboos tea to be an acquired taste. Quality matters, and it stores for quite a long time (a year or more). I pitched a high quality version that I didn't like too much, thinking it was past it's time when I actually hadn't prepared it properly, so never really gave it a fair shake.