Delko/Wolfe didn't start out well, we can all admit. Angry and still grieving over Speed's death, Eric was less than welcoming to Speed's replacement. In turn, Ryan tended to mouth off a lot to him - but even this gave slash potential! Rivalry can lay the groundwork for all kinds of interesting relationship dynamics, and opened the doorway to a whole lot of subtext and potential anger-turns-to-lust-behind-closed-doors scenes. As the series progresses, however, a thawing in their relationship is easy for everyone to see, especially after the events of 'Nailed' when Eric takes Ryan to the hospital. They start to tease each other in a much more friendly manner. There's less tension (the bad kind, that is) when they're in a room together. They even end up wearing matching colours sometimes! And all this, of course, is without even mentioning the way Ryan behaved when Eric nearly died after being shot, how he almost attacked the shooter, and all the banter between the couple. Whether they're rivals or friends that are secretly smitten with each other, the Hardy Boys make a wonderful potential pairing that while unlikely to ever be shown on TV, have still managed to draw fans from all the world.
The pairing that time forgot...pre-Hardy Boys. This couple had a very close friendship before Speed died during a shootout when his gun jammed, and Speed was the one who 'hazed' Eric when he first started work as a CSI. This pairing has the lovely option of being purely a deep friendship, or an actual relationship - both provide reasons for the way Eric so obviously resents Ryan when he replaces Speed. This couple hasn't got a very large fanbase, but often crops up during Hardy Boys fanfiction.
Horatio was the one to give Ryan his big break into CSI, and since then Ryan's been trying to do his best to emulate him, from the way he handles his cases, to the way he dresses (from t-shirts to suits!). Ryan also tried desperately to get attention from Horatio by driving off to present him with the evidence Eric had found in the water, leaving Eric behind in his haste. In turn, Horatio has tried to protect Ryan as much as he can from the politics of the CSI, such as when Ryan lost his temper and shoved an officer evicting people, or when Ryan froze during a shootout. There is also a certain amount of betrayal involved in this pairing - when Ryan lied to Horatio about the man he owed poker debts to, it resulted in him being fired after Horatio learnt the truth, and being warned that he will be watched very closely after he convinces Horatio to give him another chance. A hurt Horatio? Once bitten, twice shy perhaps.
Visibly crushed, if not broken, after Speed died beside him during the shootout, Horatio has been very focused on gun safety ever since, which was one of the reasons why he hired Ryan Wolfe as Speed's replacement. Afterwards, Horatio even ends up suffering from dreams where he is the one whose gun misfires. Just nightmares about a possible situation one day? Or a guilty conscience for not niggling his partner more about gun maintenance? Would a man usually be so distraught over a colleague's death, even if they were close friends? This is a very popular pairing in the CSI: Miami fanbase, and you can find a lot of older fanfiction dedicated to this pairing.
Not a very well known relationship, this builds on the strong ties of friendship between all three men, as well as the fact that it combines the other pairings of Speed/Horatio and Speed/Eric. There is little evidence of this threesome in the actual show - fans just seem to have put their favourite characters at the time together.