I heard "Cherokee Shuffle" at a jam last weekend: I guess it's fairly standard in the old timey/bluegrass repertoire, but it was quite new to me, except for the bits that resembled Stan Rogers' "The Wreck of the Athens Queen." As one of the fellows who introduced it to me explained, it is rather unusual in that the first part consists of a standard eight bars--or sixteen, if you will, since, conventionally, the eight bars repeat--but the second part is ten bars (twenty, with repeats). So I'm in the middle of learning my first "crooked" tune. There are no end of versions on YouTube; here's one of my faves so far:
Rather along the same lines, on the same occasion, I was told about this very useful website: The Old-Time Jam. It has backing tracks, and a fair amount of demo tracks, too, for most the of the standard tunes in the Old-Time repertoire, so when you can't get to a jam, you can, at least, have a virtual one.