I've never used Colloquy, so I can't judge its quality. According to its product page, it supports multitasking.

On my iPhone 4 and iPad, I can switch back and forth between my frequently used apps (NetNewsWire, Instapaper, GoodReader, Evernote, Omnifocus, Elements) and they rarely have to relaunch. When I return to an app, everything is how I left it.