Since I don't know all the Anime you have watched, I'll just name whatever comes to mind for Comedy/Romance/Slice of Life.
Welcome to the NHK - The anime is very funny at times, its basically about a NEET who ends up having a girl trying to help him to be normal. It gets more/really emotional near the end and yes it is a Slice of Life. If you watch enough Anime, you should get the terms and references they use good enough. Artwork might be kinda older than modern Anime but it's a really good series.
Bakemonogatari - Not a Slice of Life since it's a supernatural Anime but it's pretty good on the comedy and the romance comes in a bit later. It's a SHAFT Anime so expect randomness.
DN Angel - Fairly old anime. Again no Slice of Life since magic related events occur. Basically about a teenage boy who has transform into another person for some reason I can not remember. The romance is really messed up in this Anime, as in it's all over the place, such as she likes him but he likes her but she like him when hes transformed but he doesn't like her cause he likes someone who use to look like her. Lolwut?
Kimi ni Todoke - I've never finished the series so I can't say to much. It's a Shojo. From what I've heard, its one of the 'better' shojo's you'll find that are less known. IIRC, it's about a girl who looks scary (looks like the girl from "The Ring") and some really popular guy everyone likes starts getting into her life/talking to her/etc. Not sure if you'll like the artwork but it is a recent anime (2009~2010).
Special A - It's Kaichou wa Maid-sama in a alternate and different universe. Characters are literally the same other than the main female protagonist not being a maid in this one. I believe theres less bishounen scenes as well, as in "glowy and sparkly background" scenes.
Honey & Clover - I haven't fnished S1 yet since I stopped watching when our On-Demand was taken off. Anyways, from what I've watched so far, and is all the genres your looking for.
Ef Tales of Series - Now this would probably be one of my top recommendation for the genre. The series is known very well for it's unique and spectacular artwork and quality and it's drama it holds. I haven't seen too much of it but I saw some episodes while my sister watched the series. She was glued to it. It's a SHAFT Anime but don't expect anything like their usual work.
I could name more but having trouble since I just woke up recently.
Bolded ones are the most recommended, that I can think of off the top of my head.
/sad you dropped Baccano, but hell, I've dropped over 70+ series.
Now if I was wrong and you weren't looking for more of a Romance genre anime, since the ones I listed are mostly Romance focused, and looking for something more Comedy (since Slice of Life isn't really a genre, has been debated and is pretty much similar/same to romance/drama).
Gintama for the win. Has every genre you can think of. And references are the best. They even have Death Note parody... when eating sukiyaki.