is there a Google Talk (gChat) client for iOS that:
- does not prevent messages showing up in other clients
- does not alter or send messages, add signatures or other spam?
You can use Hangouts This is new version of Google Talk and official google product. You don't have to rely on third party products.
IMO messenger seems to be a bit better, at letting the message get to other clients as well
You can use Vtok where you can do chat, voice and video.
- Free video and voice calls to all your Google contacts over Wi-Fi and 3G
The app Verbs is a great chat client (think Adium for iOS). I use it with AIM and Google Talk and it works great.