For since the creation... men are without excuse 18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in
  unrighteousness;
  19 Because that which may be known of God is manifest in them; for God hath shewed it unto them.
  20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even
  his eternal power and Godhead; so that they are without excuse:


I had this discussion in small group about how everyone undoubtedly knows who God is through creation (verse 20). But when "they are without excuse" does that imply that those who have not heard the gospel, but know that there is God, through creation, can be saved? 

The questions arose amongst the group on whether or not people in this situation can be saved without hearing the gospel? Or are they presented with the gospel in a different way (not ways of spreading the word)? Or is there something wrong/missing?

A friend of mine did quote a passage from the book "Radical" by David Platt that when we ask the question about how people in 3rd world countries can be saved if they were never given the chance to hear about the gospel. Platt tells us that the problems lies within the question itself, that by asking it assumes that these 3rd world country people who have never heard of the gospel are innocent, when we are all sinful in nature.

But going back to my original question, referencing verse 20, are we all "without excuse" even if we have not heard about the gospel? Is there another way the gospel can be presented?
As I'm sure you know, if you continue to read on, you will eventually come to Romans 2:12, which reads: (KJV)


  For as many as have sinned without law shall also perish without law:
  and as many as have sinned in the law shall be judged by the law;


and Romans 3:23


  For all have sinned, and come short of the glory of God;


Assuming that this is true, and also that Christ was not a liar when He said


  I am the way, the truth, and the life: no man cometh unto the Father,
  but by me


and also assuming that Scripture is the inspired, inerrant, infallible Word of God, we must assume that people who have not come to Christ, and know nothing about Old Testament law, much less salvation through Christ are lost.  The only way to reach them is by getting the Gospel to them, and having them understand, repent, and turn to Christ for salvation.

The general thrust of your question has been answered here and here as well.