1. Fastest back button: [ Back button works immediately. Probably it caches the pages in memory but who cares...] This specially helps me playing browser based massive multilayer games ( You know one second delay might means a lot in your bad times )
2. Speed Dial: Ok ok. Other browsers do support it. Still there are some features like making it highly customizable keeps Opera apart.
3. Notes: You can keep notes in your browser. and you don't need an extra plug-in for it.
4. Opera turbo: Admit - We all have slow Internet connections here in India. Don't we? Turbo makes highly compressed page and a little bit reduced image quality to fight that to 80%.
5. Opera links: Keeps your bookmark with you... wherever you are. [Except inside mariana trench probably ]
6. Ctrl + Z works: It reincarnate the closed tab. It is there with other browsers but not with fav ctrl + z.
7. Go to web address: Have a link in a page but not hyper-linked? Just right click ( or double click ) and select "Go to web address".
8. opera:config: Present in Firefox [about:config] but not in so organized and friendly manner.
9. Most perfect in following web standards: Only living browser with score 100/100 in ACID 3 test.
1o. Easter eggs n more: Till now I found .
a. Type /. in the address bar. It will take you to slashdot.org.
b. opera:drives will show the drives with directory ad all.