In Iberia, the conflict between the Christians and Muslims (some parts of which were considered part of the Crusades (e.g., the capture of Lisbon was regarded as part of the Second Crusade), but extended before and after the Crusades) may have had some impact on both sides, with the Christians adopting various types of light cavalry and infantry (jinetes, almoghavars), and some European armors and crossbows being adopted by the Muslim powers.

However, the Crusades to the Middle East seem to have had surprisingly little impact on warfare within Europe.

Since it's a little hard to say "here are all of the changes to European warfare that the Crusades didn't cause!" I'll just give a few quotes:

If we can point to any modifications introduced into European warfare by the Eastern experience of the Crusaders, they are not of any great importance. Greek fire, if its composition was really ascertained, would seem to have had very little use in the West: the horse-bowman, copied from the cavalry of the Turkish and Mameluke sultans, did not prove a great military success: the adoption of the curved sabre, the ‘Morris-pike,’ the horseman’s mace, and a few other weapons, is hardly worth mentioning. On the whole, the military results of the Crusades were curiously small. As lessons they were wholly disregarded by the European world.

-- Charles Oman, The Art of War in the Middle Ages, 378-1515

In all these matters the Franks showed a cerain continuity of practice on the field of battle, but there were changes as well. From the time of their first meeting with the Turks, the Franks recognized that they were faced by new tactical problems, and that adjustments to their normal military methods were necessary. They saw that they must stand firm in the face of archery and encirclement, ignore the temptation offered by the Turks' simulated flight, preserve their solidity and cohesion until they could choose the moment at which to deliver their charge with the certainty of striking into the main body of the enemy.

-- R. C. Smail, Crusading Warfare 1097-1193

Although the environment into which they were moving was unfamiliar, it was inevitable -- and indeed desirable -- that crusading armies would stick to tried and trusted methods of fighting. The timespan of individual Crusades was far too short to make any serious alteration.

-- John France, Western Warfare in the Age of the Crusades, 1000-1300

The Crusaders did adapt within the Middle East to the unique problems they faced, such as mounted archery (their adaptations were predominantly applications of existing methods of Frankish warfare -- use of crossbows in conjunction with spearmen -- and the hiring of some local auxiliaries (Turkopoles)), but they didn't really do much to apply these adaptations to facing enemies who didn't fight like steppe nomads, nor did they really import much militarily from the Middle East to Europe.

One set of innovations that did apparently make it back to Europe had to do with certain developments of military fortifications. It's not really part of what I've studied but my understanding is that innovations made in crusader and muslim castles and defenses were then brought back to Europe. T.E. Lawrence actually wrote his thesis on the subject in 1910 which has been reprinted in book form and entitled simply "Crusader Castles."

I'm afraid I haven't read it (as I said, sort of out of my field of study) but it's one area worth exploring. Other, non-military architectural advances seem to have come out of the east at this time. Most of what I've read on that comes out of Robert Byron's tour of Persia in the 1930s in "The Road To Oxiana".

In both cases I'm sure there's more up to date information, and I'm sure someone around here might be more helpful.

This wikipedia article isn't very well sourced but seems to agree, if that's at all helpful, pointing to things like an increased number of defensive towers and arrow slits, as well as increased complexity of design: http://en.wikipedia.org/wiki/Castle#Innovation_and_scientific_design_.2812th_century.29