A link to links & a big fat THANK YOU!

I've been updating my Important Links post periodically, and I didn't mention the changes because I assumed that if anyone wanted to know what was new, they'd just go to the post and find out (I change the font of new stuff to bold & italic so that it's easier to spot). However, I must make a special mention of my Important Links post today, mainly because I believe the two new links I've added might be truly awesome, so awesome that they should have an additional post about them.
1. GMATClub has launched a new GMAT Math Book Open Project, which I think is a fantastic idea. Currently, you can find DETAILED chapters on Triangles, Polygons, Probability & Combinatorics. Other topics in the book are links to Sequences & Series, Word Problems, etc. OMG!!! :-)
Edit: I've just begun going through the Triangles chapter in this, and it's unbelievable! Don't need to try looking for any another source of Math theory!!! Seriously.
2. GMATClub has also added the Question of the Day feature!
Wow, I think they should probably pay me for "advertising" this! Haha...Anyway, what I really like about sites like GMATClub is that they seem to truly want to help out students, the part about all these great *free* features being the key! That's why I like BeatTheGmat too. Just the number of helpful GMAT & MBA related articles they post daily!!! And then there's MGMAT. Although most of their stuff is paid (they're basically paid classroom tutors!), they don't behave like maniacs trying to put a price on every single piece of advice, question, or solution they provide. Go check out their forums and MBA Resources pages if you don't believe me.
I guess a big fat THANK YOU is in order for these sites and the people who contribute to them!!! :-)

PS. I should atleast get paid for the amount of effort it took to provide relevant links in this post! ;-)

An Important Sequence & a CR link

Here's a type of Sequences question I wasn't aware of, till now.

Repeating Patterns

Many times, repeating patterns will yield a remainder question.

The first term of a sequence is  -2 and the second term is 2. Each subsequent odd term is found by adding 2 to the previous term, and each subsequent even terms is found by multiplying the previous term by -1. What is the sum of the first 669 terms?

Clearly, we are not looking to enter all 669 terms and see what the last one is. But, we can do a few and check out the pattern.
n = 1, = -2
n = 2, = 2
n = 3, = 4
n = 4, = -4
n = 5, = -2
n = 6, = 2
Since we can see that the pattern will repeat every 4 terms, we can solve for the remainder after dividing 669/4. Since 4 goes into 668 evenly, we know that the value will be equivalent to that of the first term, which = -2.

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Also discovered a whole host of useful GMAT CR articles on BTG. Read the first two (in chronological order) and found them pretty useful. Even assumptions are of two types: sufficient and necessary! And the question type (by a subtle change in wording) can change the answer! Damn. Those 2 are definite re-read material.