Assuming you want a cloud-based team chat service with mobile apps and no limitations on searchable history, these days (June 2015) you've got a number of pretty good options.
FREE Both HipChat and Slack, the most popular products in this space, use your chat history as an upgrade trigger—you have to pay to access history over a certain number of messages. Some people think that's OK, but keep in mind that Slack and HipChat replace internal email. Now imagine not being able to search your email past a certain number of messages.
A number of services offer unlimited history for free.
Fleep — see https://fleep.io/pricing Fleep doesn't have the concept of named, persistent rooms visible to your entire team. Instead, you can create groups by adding people explicitly, like in Skype. The service has an API and has the best integration with email of any product in its class.
Gitter — see https://billing.gitter.im/ You can have up to 25 people in a private Gitter room for free. The services is tightly integrated with GitHub, and currently only GitHub authentication is supported.
Glip — see https://glip.com/pricing Glip became free (for our purposes) after it was acquired by RingCentral in June of 2015. Conceptually, Glip is very close to HipChat, but it also comes with a slew of project management features, such as tasks and team calendar.
ChatGrape — see https://chatgrape.com/pricing ChatGrape is conceptually similar to Slack—it has completely isolated teams with named, persistent rooms. ChatGrape has a number "deep integrations" that make it very easy to share outside knowledge (web results, documents, code-related stuff) in chat.
Word of caution: If you're using a free service, don't be surprised if it shuts down. Startups that try to compete with powerful incumbents on price face harrowing uphill battles that rarely end well.
Flowdock — see https://www.flowdock.com/pricing Flowdock will cost a team of 25 $75 per month. A major downside of Flowdock is the lack of search for 1-1 history.
In summation There are many alternatives to HipChat! A surprising number is completely free, with some having a better feature set. If you don't want free services to go away, pay them if you can.
Pie is a work chat app available on web, mac app (and very soon on mobile) that helps you get to the point faster. Pie makes a mini-chat room for everything you want to discuss - from links, files, questions, images, to what’s for lunch - so every conversation stays on topic. Totally prevents any unnecessary clutter of messages that gets important information lost - like how normal chat is.
Other than just chatting with your coworkers, Pie makes it easy to chat with people outside your company - be it chats that you need to involve partners, agencies or your clients.
Oh... and it's completely free too :) Since I work at Pie - should you have any questions about it please let me know. I will be very happy to help.
Disclaimer: Like most of the other participants in this thread I work for the company I recommend.
If you are only looking for a good chat solution with file upload, room management, search, etc. there are hundreds of options to choose from.
ChatGrape is unique in the way it integrates services, protects your data and enriches your messages.
Deep Service Integration Almost every chat solution allows you to integrate external services like Google Drive and Github. But their integrations are limited to posting the last activity ("has created an issue", "has uploaded a file", etc.) to your room - just like IRC-Chats did over two decades ago.
ChatGrape integrates them a lot more intelligent and allows you to reference files, appointments and issues in an autocomplete as you type your message. This eliminates misunderstanding and boosts your team communication speed, so you can work on the real tasks.
Protecting your Data While HipChat has some debatable privacy practices (Who can view chat history and files?) we are making data security and privacy one of our biggest strengths.
We are soon rolling out a feature that allows you to start encrypted chats that "forget" your messages after a certain time frame.
We force every browser to use SSL Encryption between 128 and 256 bits
We are implementing security measures that will make it impossible for us to browse through customer data without their permission
Enrich your messages Searching for old messages is still a pretty distressing experience in many chats. We recently received a research grant from the FFG (research department in Austria) to automatically label your conversations based on their content. This allows us to organize your ideas, todos, questions, etc. by using custom algorithms. So you will be able to - for example - search through last week's decisions, or get custom summaries on your team's communication.
We are currently in early access, so you can use ChatGrape completely free until we have rolled out all the features. Give us a try! -> ChatGrape - Communicate efficiently.
The team I'm working with has recently made the big move and switched from HipChat to Slack, you can read about the upshot at: Why We Switched From HipChat to Slack (spoiler: we're actually going to stay with Slack for longer).
We build and use Flock.co - it has completely replaced email for us.
It's totally free, works on all devices and you can use it for unlimited users. No advertisements, no pricing plans, no catches. Have a quick look at the website - http://flock.co