[Maédhros]

He could immidiately dismiss the thought of it being one of the Nine, Seven or Three. And what would the chances be of a hobbit picking up the long lost One Ring? The chances of him finding a "lesser" ring would probably be bigger.
I think Gandalf did what he could. After TA 3001 when he picked up his suspicions, he went around hunting Gollum for a while as well. And he might also have gone to other places to search, mainly Rivendell, like someone said.

The sad thing is that his suspicions came in 2941 and he acted on them in 3001. He did what he could, he just waited for 60 years.

Saruman was, after all, Gandalf's superior, and had studied the rings a lot. Gandalf had at that time no reason to mistrust Saruman.

This is interesting.
From LOTR

That was the first real warning I had that all was not well. I told Bilbo often that such rings were better left unused; but he resented it, and soon got angry. There was little else that I could do. I could not take it from him without doing greater harm; and I had no right to do so anyway. I could only watch and wait. I might perhaps have consulted Saruman the White, but something always held me back.’
‘Who is he?’ asked Frodo. I have never heard of him before.’
‘Maybe not,’ answered Gandalf. ‘Hobbits are, or were, no concern of his. Yet he is great among the Wise. He is the chief of my order and the head of the Council. His knowledge is deep, but his pride has grown with it, and he takes ill any meddling. The lore of the Elven-rings, great and small, is his province. He has long studied it, seeking the lost secrets of their making; but when the Rings were debated in the Council, all that he would reveal to us of his ring-lore told against my fears. So my doubt slept - but uneasily. Still I watched and I waited.

Gandalf suspected Saruman for a long time, otherwise he would have consulted with him. So the supposed no-reason not to trust him is void. Look at that point in time in which Gandalf had strong doubts about Bilbo's ring, but as yet did nothing. And the sad thing is that Gandalf had the information at that time that Bilbo's ring was indeed Sauron's Ring.
From LOTR

The memory of words at the Council came back to me: words of Saruman, half-heeded at the time. I heard them now clearly in my heart.
` "The Nine, the Seven, and the Three," he said, "had each their proper gem. Not so the One. It was round and unadorned, as it were one of the lesser rings; but its maker set marks upon it that the skilled, maybe, could still see and read."

When did this Council occur? In 2953 TA, just 11 years after Bilbo had returned to the Shire with his ring. OOPS.

Bilbo's ring seemed very harmless. He stole it from a disgusting creature in a cave under the mountains (which the creature was using to hunt fish). It can turn him invisible... None of this points anywhere near the great Ring Sauron used to enslave the Nazgul. I don't find the situation of "Oh - Bilbo found a ring. Better make sure it's not Sauron's One Ring!" plausible (even ignoring the fact that the Ring was thought to be lost forever, washed into the sea). Gandalf does say magic rings are "rare and curious," but while rare, there were undoubtedly many more aside from the Rings of Power (and though there were 20, at the least 12 were accounted for). It took the Ring preserving his youth to throw up a flag.

No, in the last meeting of the White Council in 2953 TA, Gandalf knew that the One Ring had no gems, but was made to seem one of the lesser Rings. It was with this information that Gandalf went riding fast to Minas Tirith. But he seems that he just forgot about it.

This has, IMO, sufficiently answered by NightKnight and Legolas.

Not really.

Horrible excuse? Don't throw that at me! I'm just trying to find an explanation for this situation. The Elves present (after Isildur already had died) at the Gladden Fields were Thranduil's Wood Elves, not Elves from Rivendell. So, before the Disaster had reached Elrond's ears, several weeks would have past. Maybe he sent out a small party to seek for Isildur's remains, for all we know. Maybe not. As opposed to you, I do belief also Elrond's realm would have been in great turmoil. He and his army had away from home and hearth for the duration of the War of the Lat Alliance, which lasted a total of twelve years! After returning in Rivendell there would have been many pressing matters to attend to.
When all was 'normal' again in Rivendell, Arnor, and Gondor time had passed and people probably thought it no longer usefull to hunt for remains of Isildur, guessing he had been brought to sea by the River Anduin.

Let put it this way: Isildur died in the year 2 TA. In 2643 Déagol the Stoor finds the One Ring, and is murdered by Sméagol. Look at the obscene amount of time that passed between those two events. Elrond weds Celebrían in 109 TA.
It was because of the lack of interest coupled with the incompetence of the searchers that they didn't find anything. It was Elrond himself that talked to Isildur about destroying the Ring.

Gandalf went to Minas Tirith as soon as he had the idea that the answers he sought might be there.

Now I suppose he will be chided for not thinking of this sooner.

No. Lets examine the elements one more time:

1. Gandalf felt uneasy about Bilbo's ring.
2. In the last meeting of the White Council, Gandalf had the knowledge that Bilbo's ring description was similar that of Sauron.
Gandalf had all of the information that he needed to find out if Bilbo's was that of Sauron just 11 years after Bilbo returned to the Shire. If you don't think that there is a problem with Gandalf waiting an extra 64 years, then that is ok with me, but I think that it is just plain wrong.
The logical line of reasoning to me would be:
1. Bilbo is my friend.
2. I have a bad feeling about Bilbo's magic ring.
3. Bilbo's ring description and that of Sauron are similar.
4. Go and do some research about it yourself, for the sake of friendship!

think there is evidence (already noted above) that Elves and Men tried to search for Isildur’s body. However, just because they did not find it is not proof of incompetence. Consider, they were operating in hostile territory. It is true that the local orcs had lost a good deal, but they were probably still capable of pouncing upon small parties of searchers. Later, when Saruman was searching, he probably had an understanding with the local orcs, if indeed they were not working with him. Elves and Men had no particular reason to guard the area, so Saruman was able to search the area most carefully and with security. Just because Saruman found the body does not mean that it was easy to find. It might have been that it took him a very long time to uncover it. We don’t know when the body was found. Saruman began searching in 2851. The next we hear of it is in 2939 when Sauron starts searching the area. That gives Saruman considerable time to drag an unlimited number of bodies from the river.

I guess that that is as good an excuse as any that I will hear. If the wise could not mount an effective search for the most important artifact of the Age in more than 2000 years, they have to be incompetent.