I think one of the problems in defining 'rail-roading' is that there are two seperate elements being addressed here.
One might be termed 'macro-railroading'. This is where the DM presents the players with one choice for the adventure of the evening, or has a pre-determined story arc planned for the campaign whereby one set of events _will_ follow the next, regardless of player action.
The first option is not really a problem if the players are mature enough to accept that the DM may have limited time resources to prepare for all eventualities. It is also fairly easy for a good DM to get around. In the group I played with, the DM had a vast collection of published adventures. After finishing one, he usually offered us a choice - Lost Caverns of Tsojcanth or Dragons or Wen Tseng? Sometimes, character action dictated the choice. A couple of party members had been spirited to another plane (thanks to the Deck of Many Things) and we proposed to rescue them. So he pulled out Tales of the Planes.
This way, he didn't need to wing things too much on each night, but our overall path was decided by us. With the plethora of cheap or free RPG resources on the net, it's not too hard to run something like this. (Note, though, it was a fairly Old Skool dungeon-bashing style of game, which are easiest to run like this, I think).
There is also the form of social contract implicit in gaming that the DM is going to provide an adventure for the players that is appropriate for the abilities of the characters and tastes of the players, and that the players will therefore deign to at least take the offered plot hook.
The latter type of 'macro-railroading' is more potentially more problematic, symptomatic of the DL series, and a lot of the 2nd Ed. modules. Call it the Hickman Effect

. Although some groups _do_ enjoy having a coherent storyline, in the hands of an over-rigourous or inexperienced type of DM it can easily lead to the second form of rail-roading, which is:
'Micro-railroading'. This is the 'you can't go that way' type of rail-roading that occurs during the course of play of a particular adventure whereby the DM flat-out vetoes player actions that are not in keeping with his perception of the way thigs should be run. To return to the social contract idea above, it may be the assumption that 'if you don't play in this adventure there is no session tonight', but that does not imply that '...and you must follow the adventure exactly as it is written.'
This primarily a problem with inexperienced or tired DMs unable or unwilling to improvise a tangent, or to reward creative player thinking (such as where they come up with a way to block all the orcs in with a cave-in rather than fight them all toe-toe). It can also be a problem with the campaign-arc form of meta-railroading since player choices at the micro level can seriously undermine pre-planned plats.
Macro-railroading, as mentioned above, is a large portion of the DL Dragonlance modules, especially at the point where the party is split into two groups after DL4 (one plays DL 6-9, the other DL 10-12, then they meet up for DL 13-14). It is possible to play the DL campaign without doing this, and allowing player character actions much greater meaning within the campaign (I know, I've done it).
Someone mentioned Shadowrun adventures above, and these were fiends for micro-railroading. The main problem was that they tended to work on an assumption at odds with the setting. The setting proclaims the PCs as shady, criminal types doing dirty work for anyone for money, yet most of the adventures assumed that they would take the honourable course of action. Thus each section had to have a 'Troubleshooting' section on what to do if the players don't stick to the plot.
I have two further experiences to relate.
One is that I have tried to run an 'infinite' choice campaign, proffering various rumours to the players at the beginning and seeing what they would take. It was very nearly still-born as they really wanted to be hired by the archetypal crusty old dwarf and _told_ what to do. Once it got going, it worked, but in my opinion a strong and obvious campaign opening hook is extremely useful.
Second, the published adventures that I like the most are all quite old, and are more of a tool-kit than a specified sequence. The old (original) Traveller adventures are good for this, as is the RuneQuest classic Griffin Island/Mountain. Both are maps for place, stats for people, some rumours, some supplemental information. Add players, wind 'em up and watch 'em go.