Other guidebooks

Besides Lonely Planet, I use Rough Guides a lot. The disadvantage is that they are not updated as frequently as LP, but they do have good information. They also give you a free eBook version if you buy the print book, which really comes in handy. It's an ePub version so you can just open it up in Apple or Google books (or Adobe Digital Reader).

I also like Moon Handbooks a lot, and would recommend them.

I've used Moon Travel for many trips, but am not sure if they have one for Australia.

It was pre-Covid, but I used Trip Advisor online for planning my 3+ week trip: LAX-Melbourne-Sydney-Blue Mtns-Cairns-Uluru-Sydney-SanFrancisco
I found the various forums very helpful.

I also found the Trip Advisor forum to be very useful a couple of years ago when I planned an extensive trip to Australia and New Zealand. There were some very helpful people who assisted in tweaking my itinerary.

Rough Guides
Lonely Planet
DK Eyewitness Guides
Frommer's

What I like about Lonely Planet and Rick Steves guidebooks is you know when the next edition will be available. Lonely Planet’s AU guidebook 22nd edition comes out in Sep’24.
I also like Rough Guides but you don’t know when the next edition will be available although their AU book came out in Feb: https://shop.roughguides.com/listing/?continent=AUS.
I believe Rough Guides and Insight Guides have merged. The Insight Guides book came out before COVID so that one I would not buy.
I also like to look at Foders: https://www.fodors.com/ and Frommers websites: https://www.frommers.com/.

All great advice. Thanks everyone.

Fodor’s is my go to now.

On my 2019 trip to Australia and New Zealand I used Lonely Planet.
Lonely Planet Australia was a brick (about 1000 pages if I remember correctly) but very good.
Rough Guides is also good. I suggest checking the publication dates for both and take the one that's the most recently published.