These are the sensors I want to use with the Uno rev 3
And what exactly does this do? http://www.ebay.com/itm/271139523942?ssPageName=STRK%3AMESELX%3AIT&_trksid=p3984.m1555.l2649
The first two appear to use a serial wire pair, and they suggest using SoftwareSerial library which can use any two
pins - so each sensor kit can run on your choice of pins.
The last combo board seems to use USB connectors for analog inputs and for I2C bus, for obscure reasons, but
basically packages several options in one shield - it will have fixed pin assignments since its a shield, but might well
do all you need (although it might use more pins than you have spare, always check out the pin usage before
purchase).
What exactly are pins? Sorry but I'm a still a noob 
PIns are connectors on arduino or sensor. Each wire has a pin in the end and it has to be connected to an arduino pin (normally, not all of them sometimes)
Oh I see. Thank you very much for your info
Sorry for the double post but would this have all I need to be able to connect the 2 sensors at the top of this topic to an Arduino board?
http://www.dynamodo.com/modules/development-kits/kit009-kits-arduino-starter-kit.html
Or would I be better off using the shield instead? Unless that also requires an Arduino board. But I think it doesn't.
Thanks again guys
Hawhaw:
What exactly are pins? Sorry but I'm a still a noob
In which case, might be an idea to get some basics under your belt?
Yeah currently reading the books from Make about Arduino
Will this get the actual pH value of a soil sample or will I need to do some computations? Thanks!
most sensors you need to interpret the signal that comes from it.
This may include computations and these are almost always mentioned in the datasheet.
this side has sample code - http://atlas-scientific.com/product_pages/embedded/ph.html -
And the sample code has the computation needed for it to display the actual pH value?
Read the datasheet - it is on the same page - and you know how it works :
Oh. Okay thanks!
Can the Arduino work in sync with a C program that logs the data it will get from the pH sensor?
you can send data back over the serial port and do what you want with it in any programming language
Can it log the data on a database like MS Access?
Is this possible? If so, will I need another program to make the program that will automatically log the pH value on a database like MS Access?
The Arduino can't but the program that it communicates with on the PC can.
How would I be able to do that? What code would I need? And what program should I use?
An Arduino programming forum is probably not the best place to ask such a question. Are you familiar with any programming languages that run on the PC ?