biteSMS ($8.99 on Cydia store, 14days trial with free of ads, or continue using it but it became ad supported)
It is the single best ever app I ever download, not only the best app I ever download from Cydia, but out of all the app I download from the appstore too.
Apple notification sucks, whenever you are playing a game, browsing at safari, reading RSS at your RSS app, and when a SMS pop up, I will have to close the app in order to reply it. What multitasking is this?
Well, biteSMS is the thing, all because of the Quick Reply.

Gone is the days you need to quit the app you are currently working on just to reply the SMS, and then relaunch the app again. Now this is multitasking!

Besides, not only Quick Reply. With biteSMS you can compose SMS inside any app too without the need to quit the app 1st. Just click the volume up button once, and when the biteSMS icon pop up in the middle, tap it, and you are in the quick compose mode.

You can also have a quick look on your previous messages with that particular person easily too before your quick compose or quick reply.

and finally delivery reports on iPhone!

those that always lend your phone to friends to play some game or browse will love this. Passcode Lock on SMS!

and the good old character counter so that you don't sent 2 SMS just because you typed in 161 character

Besides all the features I mentioned, some others such as signatures, contact picture on SMS, exact message timestamp and many many more.
You can always read more about it on their website
HERESo with all the features, does it worth USD9, which is around RM30? A HUGE YES! DEFINITELY!
It never crash, it makes SMS so easy and exactly how a phone should be. I hope 1 day apple will do this to their native iOS SMS app, but before that, this is the best.
Not Convinced? Try it for free! The app gives a 14 day trial with all the features it has. After 14 days, you can either buy it or the app will become app suported. If you are those who always travel, you can also try their SMS credit for cheaper international SMS. I never try it before though
What cons of biteSMS you might ask? Well, absolutely nothing. And if I am to be picky, I will say that the icon look FUGLY in pink. Luckily there's a way to get rid of it (again the awesomeness of JB), which I will post up when I am free
Value of Money: 100/10 (no, not a typo

)
Features: 10/10
PS: I never use iRealSMS before, but biteSMS do it greatly for me