Oh man, lets see. In the past 3 or 4 years I've probably found 750 discs (not counting the thrashed ones I leave behind). As for what I find most it varies based on what's hot at the time. DX valks have always been popular and I find them regardless of where I am. Pro wraiths were very hot for a time and I found like 20 in a year. Star wraiths, same story. In '04 and '05 the champion orc was the big new driver and I still have most of the 40 I found during that time.
Here's a list of what I tend to run across most often overall:
1) DX valkyrie- Everyone seems to throw these damn things.
2) Champion Valk- Same as above. Very numerous.
3) Champion Beast- old mold or new, I find tons of these.
4) Champion Sidewinder- everyone seems to throw them and their aim universally sucks.
5) Champion orc- very hot a few years ago and now hot again.
6) Champion starfire- As mentioned above these things are becoming way popular. I find them everywhere I go now.
7) Star/pro wraiths- Still find these pretty steadily.
Notice there are no discrafts on this list. They are making strides in popularity here, but not to the point that I find any one model very often. I did find about 15 ESP surges the last 2 years though.
As far as mids and putters go I find them far less frequently than drivers. The most popular mid is the Z buzz and putter is the DX aviar.
To find all these I just wade around (in waders of course) and feel them with my feet. As long as there aren't big rocks or other debris in the way its really easy to to but takes time and patience to do a thorough search. The late fall and spring are actually the best times to search because in the summer you get everyone else diving in the lakes too, which thins out the discs considerably.