There's a few good tips on the sticky, but here's some of my faves on my S2...
Get Tapatalk free from the Samsung App store. I think it's R23 on the Android market, and it's great for myBB and other forums. Otherwise, apart from previously mentioned Asphalt 6, the Samsung App Store is pants
On the Android Market, games wise, Stupid Zombies is a lot of fun and free, and of course there are 3 free Angry Birds games (free because they have ads, but they are not really noticeable and don't spoil the games) and you can also get Cut the Rope for about R8 I think it was.
Juice defender is good for extending your battery, no expertise needed if you use the default setting, and best of all it comes with a widget which toggles your data of and on when you lock the screen. You can get the pro versions also if you want to fiddle about more)
ConvertPad for all sorts of measurements and volume conversions.
Battery Widget shows you the percentage of battery left at a glance.
Alarm Clock Xtreme Free escalates your alarm volume and is much nicer and more customisable than the Samsung clock.
The Supersport app is also great for sports news and latest scores.
Just a few of my favourites and all free apart from Cut the Rope
