We need more...
Some of us parkour'ers and Boomo'ers have already finished our achievements. Some of them, if Staff are either having trouble implementing or can't think of any:

Infected:
Win 10 Games as Human - 1000
Win 15 Games as Zombie - 1000
Survive to where you are the last human in the game - 750

Laser:
Get a Killstreak of 5 - 500

Airship:
Kill the Giant on (Forgot which map) - 500
Collect loot from 5 chests on one map - 750
Kill 100 mobs in total *** to go! - 750
Find an Emerald in a chest - 500
Find a Diamond in a chest - 250

Dungeon:
Find 5 Chests - 250
Find 10 Chests - 500
Find 20 Chests 1000
Find 100 Chests - 5000
Find 500 Chests - 25000
Kill a Witch - 250
Kill another player - 500

Parkour:
Complete all parkours 5 times - 50000

Creative:
Build 500 blocks - 250
Place 250 Utilities - 250
Build a fully functioning Beacon - 500
Have 15 players look at your plot - 500
Place 1000 Utilities - 1000
Build 10000 Blocks - 5000

Skyblock:
Obtain a piece of cobblestone - 250
Obtain 100 Pieces of cobblestone - 750
Cut down your starter tree - 250
Find an apple - 250

Wild:
Find a Desert Temple - 750
Find a Jungle Temple - 750
Find a Dungeon - 5000
Kill a Wither - 2500
Find another player and kill them - 500

Towns:
Join an Alpha town - 250
Join a Beta town - 250
Become an assistant in a town - 750
Become a Co-Mayor in a town - 1000
Create a new town - 10000 (As some money to put in the bank for it)

Spleef:
Win 5 Games - 500
Win 10 Games - 1000
Win 50 Games 5000
Use a Diamond Spade in Spleef - 500
Join a game with more than 10 players, and win - 2500

KitPvP:
Kill a player - 250
Go on a 5 player KillStreak - 500
Go on a 10 player KillStreak - 1000
Go on a 20 player KillStreak - 2500
Go on a 30+ player KillStreak - 10000
Use all of the kits - 250
Find all 4 of the secret Explorer kits - 500

CTF:
Win a game - 750
Win 5 games - 1000
Win 5 games in a row - 2500
Play 50 games - 5000
Join a game with more than 20 players, and have your team win - 7500

HG:
Kill a player - 250
Win a game - 750
Win a game with all slots full - 3000
Win 10 games - 1000
Win a game without losing any Health - 2500

Boomo:
Kill another player with your TNT (is it possible?) - 750
Win 5 games of Boomo - 1000
Win 10 Games of Boomo 1500

Plus the Mega Achievement:
Win all Achievements - 100000

Achievements should also be reset, if you have completed all of them - Leaving you all the time in the world to get the Mega Achievement. Also, the reason there is a reset is to let people do them over again.

That is all, and I'm excited to see what you have to say! :)