I have an HTC One M8 and the following apps are my favourites.
I havent included any games as they are very objective.
1. Cameralert. This app can work in the background as you drive to alert you to Safety or speed cameras. The original app and database is free to download. You can subscribe to Pocketgps world on an annual basis to be sent weekly database updates. It works perfectly with the Car mode on my M8 so that both run at the same time, perfect. I had originally subscribed to pocketgps world for updates to my Tom Tom stand alone sat nav, this one subscription gives me free updates on my phone as well so worth considering.
2. FreediYT downloader. Got this originally from Amazon app store as a free app of the day. Allows you to download videos from you tube and save them on phone. Also allows you to save video purely as an mp3 file. Really handy if you want to find a song.
3. Handcent SMS. like the fact that it will send long mms messages as an mms rather than converting it to an sms and you getting charged by your carrier.
4. Myfitness pal. Great app if you are looking to lose weight. You input your age, height, etc. Tell it what weight you want to be and how much you would like to lose each week. It will then calculate how many calories you can eat each day to achieve this. Has a great database of foods to make entering foods easy and you can also scan most barcodes. It also remembers your regular items to make selection easier.
Great app that really focusses your mind and stops you taking that late night snack if it is going to put you over your daily goal. It also syncs with fitbit which helps as fitbit in the UK does not have a database so anything you input to Myfitness pal pulls through to Fitbit. Any extra exercise captured in fitbit also carries over to myfitness pal showing if you can eat extra that day because of it.
5. Passwordbox. All the recent scares made me look into setting more complex passwords as i tend to use the same one on lots of things. This app is excellent. Set it up using one complex password that you will remember. You can then generate really complex ones and reset all of your internet based passwords. It syncs across your pc, phone or tablet. Once set, everything is encrypted and only by being able to access the app or add on on your pc, phone or tablet can your password protected websites be accessed. The chances of someone randomly working out my password for my online banking are now way more remote. Great app.
6. Mysuperlist. If i am looking for a particular item (stocked in a supermarket), i can type it into this app and it will look at all of the top supermarkets and show me the current price in each so you can see instantly who has a deal on.
7. Shazam. I love music and if i am out and about and hear a song i like.
Quick shazam and it will tell me the name and artist, also keeps a note of it so i can look to download it later.
8. LockScreen by lidroid, great wee on screen widget, one touch and screen locks rather than reaching for power button.
9. Weq4u. avoid paying hefty charges for 0800 or 0870 numbers. I have saved a fortune with this.
10. Whatsapp, great for sending picture messages using data or wifi and avoiding picture message charges from your provider.
11. Final one is Gemini calendar. Great calendar app, but what swings it for me is that i can have a widget in top section of screen with up to 8 lines showing upcoming appointments. Means every time i open my phone i see at a glance what i have to do. Works for me.
Hope some of these are of use to you.