What about AgITaTiNg the hell out of the tank while developing !
I thought that increased contrast, not grain?
i thought both 
increasing agitation will increase contrast, which will darken the visible grain thus increasing the perceived amount of grain. so yes, both.
no one mentioned increasing temperature which also increases contrast and perceived grain.
in past experience (rightly or wrongly), i believe leaving undeveloped film in a hot environment, such as a car in summer, tends to increase grain for me.
increasing enlargement size, decreasing format size, using a higher iso film type, push processing or using a different developer are probably the easiest ways to increase your grain.
a 35mm frame will appear grainier than a medium or large format image of the same size.
Francois is right by saying croping in to a frame it increase grain, but be careful if you go too small you'll get lousy detail and resolution.
i think delta 3200 or tmz 3200 are very grainy in 35mm. people argue that the t-grain films are perceptively grainier than conventional films. (ie 400 tmx vs 400 tx) i think its something about larger flat t-grains actually add to the grain because you are more likely to see the grains due to size. i've heard arguement the other way as well. personally i don't shoot t-grain films often because i like more forgiving exposure latitudes.
i find 35mm hp5+ pushed to 1600 or 3200 much grainier than tri-x in the same situations. push processing will increase your contrast which as i said earlier will increase your perception of grain.
darkroom cookbook says "high acutance" developers tend to increase grain (ie rodinal). hc110 is supposed to give more grain than d76. the instruction sheet for ethol lpd says you can use it at iso 2000 with hp5 for increased grain. unfortunately my developer experience is mostly limited to book knowledge. i've used rodinal and d76, but i can't really say i've looked for a difference.
hope this helps.
