Bukkit is dead. Sorry... it's true. I don't like it any more than anyone else does. Sponge looks to be a really exciting prospect, especially with its native mod/ plugin functionality, but most of us are still on 1.7.10 because our favorite mods aren't updated to 1.8 (and some of them never will be). Cauldron has folded into Sponge, so there's no real way of using Bukkit plugins on a Forge-modded server. Pretty big bummer.
But a lot of Bukkit Plugins would work just fine in Forge, if their creators wanted to make that leap (or if some plucky coder wanted to bridge the divide or make alternatives). These are excellent plugins for Bukkit, and could be just as great, if not greater, in Forge. Here are some of my favorites:
PVP Arena: Players get to choose a kit, which admins can create on their own, then dive into a battleground zone/ arena for a fight. Our old server had deathmatches, team deathmatches, CTF games, and a lot more. They were some of the most popular features on the old Waywardcraft. This mod not having a Forge alternative is criminal.
Casino Slots: No one has made a slot machine mod that dishes out items when you win? Seriously?! This mod using physical currency would be ideal; slot owners could pick which currency types their machines will accept, and what they'd pay out. Servers like mine could use mods like Minecraft Money or Artifice coins as currency. Maybe expand it with games of roulette, poker, blackjack, etc.?
Jail: How is there not a jail mod yet? As it stands we need to use ForgeEssentials and /warp a prisoner into a worldguard-protected prison. I miss the /jail command and the fact that trying to escape summoned a horde of mobs to kill you.
BlockBank: The best economic plugin ever made. There... I said it. Players could store money in bank accounts, with interest, and take out loans. A version of this with physical currency would be every kind of awesome there is.
Multiverse: The ability to make a new world and teleport into it... seems pretty simple. There are lots of mods that create new worlds, but none that I've found that let you do it yourself, with a second overworld, second nether, etc.
QuickShop: The second-best economic plugin ever made. QuickShop allowed players to turn chests into shops that sold or purchased items. There are a few alternatives to this in Forge, like Trade Booths and Vending Block, but none do it quite as awesome as QuickShop did.
Lottery+: This one goes with the Casino one, but players loved playing the lottery, and loved it more on the rare occasion when someone actually won it.
RegionForSale: Allowed admins and players to buy, sell, and rent WorldGuard regions. Great for making functional hotels, selling shop plots, transferring business ownership, etc. This would be even better as a mod, with signs for sale/ for rent signs that could be placed quickly and easily (you don't know pain until you've written command signs for residential, commercial, and industrial plots in a huge MC city, lol)