I am planning a web-based commercial application with front-end RoR and back-end PostgreSQL.
I've some confusion about RoR and PostgreSQL Edition to use. For RoR, I have Aptana RADRails installed. For PostgreSQL, a free variant is also available at EnterpriseDB.
Previously I installed a free EnterpriseDB PostgreSQL variant and it was very smooth and had professional touch. It was quite different from the one available from PostgreSQL website.
I want to know which IDE and RoR variant to use for my project. I have no idea of Ruby and Rails. I will be learning and developing simultaneously. Also, which PostgreSQL variant to use? Can these two technologies be used for a developing a commercial application?
You will do fine with either EnterpriseDB or PostgreSQL. EnterpriseDB might have a better Windows install experience, but on Linux installing vanilla PostgreSQL is a very easy process...most distros provide it out of the box. The real benefit of EnterpriseDB over PostgreSQL is Oracle PL/SQL support, some upstream improvements, and commercial support. However, you can purchase commercial support from them for vanilla PostgreSQL as well.
We use vanilla PostgreSQL 8.3 in a large (800 kloc) production ERP system. It handles it extremely well. We also use 8.4 in a number of other applications, including two Rails apps. In my opinion, you can't go wrong with PostgreSQL, and you'll be very pleased with PostgreSQL and Rails.
Regarding IDE and RoR variant...well...assuming you mean RoR version, they all support PostgreSQL. I'd personally start with the 3.0 beta, since it's the way of the future. Regarding an IDE, Netbeans is probably the best free option out there. RubyMine would be great if it weren't so damned buggy. Me, I use vim.