Oh, I know that feeling. I actually have so many characers "in progress" that I keep a list of all of them and where exactly they are in the game and what level they are at. I use a word document and everything. I like to think of it as variety. Constantly working on one specific character at a time doesn't appeal to me so if I get tired of one, I look at my list and determine what would be a good change for my next play session, and then break that character out, progress some, and then go on to the next. They all get done eventually, but they all ulitmately stall for some time when I hit Act 3 because I hate the jungle.
Here is my list right now, I think I need to update a few of them though, I sometimes am too lazy to do it. (Actually I know its missing some, because a couple characters are just plain not listed.)
In Progress:
(Keeping in mind I MP a lot so sometimes character levels don't match the quest they are on at all)
ADeadlyToxin – Poison Nova Necromancer – Level 74 – Act 3 Quest 1 – Hell
Bam_YoureHealed – Healer Paladin – Level 13 – Act 1 Quest 4 - Normal
FeralandFurious – Fury/Feral Rage Druid – Level 56 – Act 5 Quest 1 – Hell (Rushed this one a bit as you can tell by the level)
Fluffy_Bunny – Passive Amazon – Level 27 – Act 3 Quest 5 – Normal
Frozen_Sparks – Frozen Orb/Nova Sorceress – Level 42 – Act 1 Quest 1 – NM
HeWhoFlipsOut – Holy Freeze Zealot – Level 62 – Act 4 Quest 1 – NM – KTA
Lana_Kane – Blizzard Sorceress – Level 90 – Act 5 Quest 5 – Hell
Shock_AndAwe – Charged Bolt/Hydra Sorceress – Level 70 – Act 2 Quest 1 – Hell
SirRiftALot – Rift Paladin – Level 77 – Act 2 Quest 4 – Hell
Static_Shock – Holy Shock Paladin – Level 46 – Act 1 Quest 3 – NM
TheRiftReopens – Kick/Trap Assasin – Level 35 – Act 5 Quest 1 – NM (Rushed this one as well, but its actually a remake, first one died, so eh)
The_Enchantress – Enchant Sorceress – Level 62 – Act 5 Quest 6 – NM
The_Fanatic – Zeal/Fanaticism Paladin – Level 42 – Act 1 Quest 1 – NM
Zapados – Lightning Sorceress – Level 42 – Act 5 Quest 5 - Normal