What's a good client tool to access Oracle RDBMS?
I haven't found anything 'free' that works as well as Oracle SQL Developer. In the past it was pretty buggy and frustrating. I am on a 3.0 Early Adopter release now and very happy with the improvements. I am a heavy user and have had no crashes in the 3 months since going to this release. I wasn't sold on the interface early on but I am familiar with it now and very productive with it. I also make great use of the User Defined Reports -- all the SQL Queries I had floating in text documents for troubleshooting I wrap into their own custom reports. 

Toad is an option... but can be pricey. It satisfies your want-list. If you want to pay for all the bells and whistles and have to support a lot of differenct databases it might be worth it for you. 

A lot of developers  here use AllRoundAutomations "PL/SQL Developer" tool, so many in fact that we bought a site license. Single seats can be had for US$180 per seat. It fits your requirements. I have not personally used the debugger but it is a mature product, I would expect it to work as advertised.