I have spent a pretty fair amount of time here so I figured I would share my Top 5 with you guys. This is strictly my opinion so feel free to comment.
These are in no particular order, I just think they are things that a 'packer should do while here...
1. Nightlife - Lapa, Clubs, Bars - There is great nightlife here. The clubs are as good--if not better--than I have seen in my travels. Lapa is an area near the Centro where it is an endless street party with cheap beer, food, live music, and great bars, pubs, and restaurants all around. You can easily find a good bar in any neighborhood here. There are plenty of 24 hour "juice bars" that sell fresh juices (excellent!), beer, burgers, steak, chicken. Basically a full menu cheap all night long!
2. Crocovado + Cristo - Some of the best views of all of Rio are at the famous Jesus Christ Statue. It is a fun, scenic ride up the mountain in a taxi. It IS worth the price. There is also a train you can take if you want to save money and have a less scenic ride up and down. DON'T FORGET THE CAMERA!!
3. Beaches - The best beaches I have ever seen! The girls are EXCELLENT as well!
I spend a lot of time here. You can rent a chair really cheap (and umbrella too if you want...) and the same guys run you a tab for beer, drinks, food, etc. Great to work on your tan, swim, relax, enjoy!
4. Food, Eating out - Brasil is not the best place for vegetarians. I find it somewhat difficult to get veggies outside of some peas or a basic small salad. That said, the beef here is great, the Rodizios have all you can eat. My favorite was R$ 17,90 (about $8.30 US) and it had all you can eat sushi, beef, pizza, pasta, beans + rice, veggies, everything! These are all over the place. I would not pay more than $R20 for it as they are everywhere. Some of them charge more because of fancier foods like crab legs and lobster so check out the food before you blindly refuse based on price!
5. Carnival - The place is loaded with tourists but it is STILL a blast. New Orleans doesn't even touch this. There are street parties everywhere you look with loads of people follow trucks loaded with speakers blaring samba and other Brasilian music. There is more then enough alcohol (and sex) to go around. Lapa is always crazy during this time. The actual parade is worth a look as well. TIP: If you want to go to the parade then buy your tickets here. They charge a LOT less if you buy them here. You won't get the best seats but you will save hundreds of dollars (not kidding). I had the worst seats but could not complain for R$ 25 (US$ 11.60). ALWAYS sort your bed ahead of time. Bring a disposable camera because they cost $25 USD here! Carry only the money you need for the night! And dont forget to get hammered and have fun!
Whew, I know that is long winded but I wanted to cover all the bases. Hopefully someone will make good use of it!