(Sorry for my bad english)
I've been searching the best solution last month, looking for the best way to have a Front End Custom Content Post Type Creator with Custom Taxonomies and also Custom panels/fields (also Image Upload) for my users. (Also I've the difficulty of custom post types in Buddypress and Multisite so it's not becaming an easy work). I have tried some plugins but none of them works as I want. Apart of the plugins there are other possible solutions, that were not good for me, but maybe for you.. So I've been trying to modify some of those solutions and include other scripts I found googling, but I'm not a php ninja and I'm still working on it.
But I will post here some of my approachs to that:
-Plugin Front End Editor: I've not been able to Create posts, and the author says that it's something not in the road because there are "lots of plugins that do that"
-Plugin Posthaste: Too simple.
-Plugin Quick Post Widget: It's a widget and you have to create a page and widgetize it. It's too simple and only accepts posts, categories and tags.
-Plugin Event Press (sorry, don't remember why this wasn't good for me)
-TDO Mini forms: actually it's a form plugin but it can be customized in the back-end to work as a Front-end Post Publisher. Too simple for my needs.
-Gravity Forms: I've readed that this is the best solution but you have to pay for the advanced version that gives you that possibility. Did'nt try it.
-Contact Form 7: I readed that some people has been able to modify it to post from the front-end. I haven't tried it.
-Jet Quick Press: I don't remember where, but I readed that this plugin was a copy of the firstly released "One Quick Post", so I thought that it was better to go with the original one.
-At first, this "One Quick Post" looked to be great because in theory supports Custom Post Types and Custom Taxonomies, but having some problems with the steps process, I tried to learn more of it. It looks that the author actually created this "One Quick Post" only to support the creation of his other plugin "Your Classified Ads". With the version 0.5.7 alpha, now One Quick Post, for me, when I try to create a new form it doesn't create the first step and I cannot work with other custom post types as I want. Also, in "One quick post" there are options, (geolocation) that I think should be in "Your classified ads" and not in "One Quick Post"
I tried to modify "Your classified ads" to work with my custom post types, but there are a lot of files and changes to make...
Also the author is not able to update both of them as he (and we) want...
Then I've readed about some theme that have this functionality for final users. It's called P2. The Buddypress Groupblog plugin even include 2 templates based on this P2 theme for posting from the front end through a Buddypress group. But I've some different problems with this plugin and cannot be my solution.
Then I recently discovered a new Buddypress Plugin, Buddypress Docs, that I can modify to be my own custom post type, now that it is on the early stages but it will grow fast as the author is very active, Boone Georges, and he's introducing improvements every week. This one looks the most promising for my needs, but I don't know if it cover yours, because on those first stages only works for Buddypress groups but maiby it could be adapted to work in single WP.
And here I am, trying to insert custom taxonomies in this Docs plugin.
If someone knows a better working solution to give users the ability to Create a post (Custom Post Type) from the Front End, adding (predefined by the admin) custom fields and custom taxonomies, please share it. Thankyou!