"Yes, yes you can. The license allows it. Just be kind and leave a link to the original Minecraft forum thread, and a mention of the author's name somewhere."
Advent of Ascension: Xolova
“You may use it.”
Minecraft Forums message, e-mail the contact info for proof if you need.
Better Storage: copygirl
“You can use BetterStorage in your modpack, public or private.”
Carpenter's Blocks: Mineshopper
"You're automatically granted permission to include this mod in a modpack."
Chisel 2: AUTOMATIC_MAIDEN and TheCricket26
"Chisel is free to use in any modpacks, without permission."
CodeChickenCore and NotEnoughItems: Chicken_Bones
"You are welcome to include any of my mods in modpacks as long as you provide credit. My name and a link to this page is fine."
Extra TiC: Glassmaker
"You can add this mod to your mod pack, public or private, just add a link to this forum page."
Inventory Tweaks: Kobata
"Feel free to redistribute it! My only request is to provide a link to either this thread or the mod's website."
Map Writer: VectronDiablon
"You may also redistribute either in your own Mod Packs. I don't care about credit."
OpenModsLib and OpenBlocks: OpenMods
"Yes, you can use these in your mod pack ;-)"
Xeno's Reliquary: x3n0ph0b3
"Please don't email me or ask. The answer is always yes."
Streams and Farseek: delvr
"You may include this mod and API in a modpack if you provide author credit and a link to this forum thread."
Tinkers’ Construct, Tinkers' Mechworks, and Mantle: boni
“Modpacks are encouraged, feel free to do anything you like with it. I only ask that you enjoy it!”
“Stop asking me if you can include it, YES YOU CAN. That's what the permissive license is for. Just do the usual link back to this thread or my blog and everything is cool.”