Romans 1:20 For the invisible things of Him from the creation of the ordered system are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:  
21 Because, when they knew God, they did not glorify Him as God, neither were thankful; but they became vain in their imaginations, and their foolish heart was darkened. The Sin  
 
Ps.19:1 THE heavens declare the glory of God; and the firmament sheweth his handiwork.  
 
The best thing is to go from nature's God down to nature; and if you once get to nature's God, and believe him, and love him, it is surprising how easy it is to hear music in the waves, and songs in the wild whisperings of the winds; to see God everywhere in the stones, in the rocks, in the rippling brooks, and hear him everywhere, in the lowing of cattle, in the rolling of thunder, and in the fury of tempests. ~~ Charles Spurgeon  
 
Psalm 65:6-8 (Amp) Who by [Your] might have founded the mountains, being girded with power, Who still the roaring of the seas, the roaring of their waves, and the tumult of the peoples, So that those who dwell in earth's farthest parts are afraid of [nature's] signs of Your presence. You make the places where morning and evening have birth, to shout for joy.  
 
Does not all nature around me praise God? If I were silent, I should be an exception to the universe. Does not the thunder praise him as it rolls like drums in the march of the God of armies? Do not the mountains praise him when the woods upon their summits wave in adoration? Does not the lightning write his name in letters of fire? Has not the whole earth a voice? And shall I, can I, silent be? ~~ Charles Spurgeon  
 
1 Chr 16:31-34 Let the heavens be glad, and let the earth rejoice: and let men say among the nations, The Lord reigneth. Let the sea roar, and the fullness thereof: let the fields rejoice, and all that is therein. Then shall the trees of the wood sing out (rustle in praise) at the presence of the Lord, because he cometh to judge the earth. O give thanks to the Lord; for he is good; for his mercy endureth for ever.  
 
I need not shout my faith. Thrice eloquent are quiet trees and the green listening sod; Hushed are the stars, whose power is never spent; The hills are mute: yet how they speak of God! ~~ Charles Towne  
 
Touched by a light that hath no name, A glory never sung,  
 
Aloft on sky and mountain wal,l Are God's great pictures hung. ~~ John Greenleaf Whittier  
 
Isaiah 55:12 For ye shall go out with joy, and be led forth with peace: the mountains and the hills shall break forth before you into singing, and all the trees of the field shall clap their hands.  
 
I love to think of nature as an unlimited broadcasting station through which God speaks to us every hour if we will only tune in. ~~ George Washington Carver  

(some caveats about hearing God's Voice)
 
Thy bounty shines in autumn unconfined, and spreads a common feast for all that lives. ~~ James Thomson  
 
I like autumn best of all, because its leaves are a little yellow, its tone mellower, its colors richer, and it is tinged a little with sorrow. Its golden richness speaks not of the innocence of spring, nor of the power of summer, but of the mellowness and kindly wisdom of approaching age. It knows the limitations of life and is content. If you have never heard the mountains singing, or seen the trees of the field clapping their hands, do not think because of that they don't. Ask God to open your ears so you may hear it and your eyes so you may see it, because, though few men ever know it, they do, my friend, they do. ~~ McCandlish Phillips  
 
Is.44:23 Sing, O ye heavens; for the Lord hath done it: shout, ye lower parts of the earth: break forth into singing, ye mountains, O forest, and every tree therein: for the Lord hath redeemed Jacob, and glorified himself in Israel.  
 
Some may say, "Well that was for then, but now that doesn't happen any more. Such a statement is either revelation or speculation. If they are claiming revelation, then they are claiming to be the only one who can receive revelation at the same time they are claiming that revelation is impossible. That is not rational. If they are claiming speculation, then their thoughts are as valid as anyone who pulls information from the air. In other words, they are telling you not to beleive them.  
 
When any person reads the Bible, God speak to them through the Bible. The Bible is not a god, but the true God does speak to every person who reads the Bible. The problem is that so many people who read the Bible are blinded by their own theologies so that they cannot see what is written, nor can they hear God's voice.  
 
For those who have actually stood in the presence of God seeking His face, we know that God speaks. God directs. He mainly speaks through the Body of Christ in the present. We know that no person can so much as sincerely say that Jesus is Lord except by the Holy Ghost speaking through the person. God has restored prophecy to the Church. He has restored the word of knowledge and the word of wisdom. He has restored the office of the apostle and the ministry of the prophet. God speaks through all of these with great authority and accuracy.  
 
There are false prophets and false apostles and false gifts, but the false does not make the true any less true. It is possible to discern the real from the false. God has promised that if we seek HIM, we will find Him. Whoever has a willing heart will find the real and the genuine and will not be deceived by the false.  
 
God does not show visions to every person. He doesn't seem to always give visions to anyone. He does, however, give visions. And He speaks through dreams. He speaks through a still small voice. God speaks through His creation. The Bible and experience show that to be true.

More Scripture through which God says that He speaks to us and leads us.

Here is the answer that was given to one professional Atheist concerning this issue: http://www.SeekFind.net/Questions_and_Answers__Atheist_Asserts_the_Revelation_Is_Unreliable.html