I have this thread running with mod suggestions. It may have ideas for you.
I also have this thread with a suggestion for a mod. I think it would be fantastic if someone made it.

I need a mod, which doesn't exist yet, so if you want to make it for me, I would highly appreciate that! Just contact me if you're up for the idea. Thanks!

Advent of Ascension (Its better to try this all by itself because its a huge mod, for adventures and stuff)
Optifine
MorePlayerModels
CustomNPCS
Decocraft 2
techguns
rival rebels
Metroid Cubed 3
Fnaf universe
World edit
Malisis mods
Chisel (decorative blocks)
Chisel and bits (Smaller blocks, just try it out)
Emoticons by MChorse (Has animated emotes or dances and etc)
Electroblobs wizardry
Advanced lightsabers (It has way more than just lightsabers)

Ill list some more later

What type of modpack are you looking to make? If it is a public pack, make sure to gets permissions from mod authors.