I wholeheartedly echo mgbills post. Scour the forums - and the two links I will provide and you will find all the info that you need. Over the years Garcia used JBL D-120's, K-120's and E-120's. The choice of JBL speaker, along with your choice of pickups and guitar electronics, a combo amp, or pre-amp/power amp/speaker cab setup and an idea of what tonal "era' you are most closely trying to replicate will get you pretty close.
Effects pedals, whether J.G. used the models you are looking into or not, just add color to your tone - I advise that you nail down your clean tone and then determine which effects you want to add some color. Remember, great musicians can play through just about any combo of gear and you can tell who it is that is playing, The Melkweg shows on 10/15,16/1981 are a prime example of this. Having the correct gear is part of the equation. But your right and left hand technique are the #1 key. So practice, practice, practice.
Youtube is a great resource for sound samples of pedals, speakers, pickups - just about any gear you can think of. You can spend $1000's and build an exact clone, but you can do very well on a budget. Thee is a youtube video I will post link to (I believe it was posted by a member here) - he uses a Hughes and Kettner Blues Master pre-amp (out of production but they pop up every now and then on he used market for under $300 - he has it matched with an Alesis Nanoverb, a QSC GX3 power amp and a 1x12 JBL E-120 cab and his Garcia tone is fantastic.
Great (and required) info:http://wald-electronics.com/http://www.dozin.com/
Good luck, research, practice, research, practice - rinse and repeat.