These are in some kind of order, but not strict...
Coyote Point (Lake Casitas, CA): This is where I first started playing. I've played course since that are bigger, some that are harder technically, but this one's my first love. The course is technically demanding, plenty of elevation changes up and down, and plenty of water hazards. You earn par on this course. Aside from that, it's one of those courses that's loaded with places where you're hiking along, look up and realize that you're in one of the most beautiful places you could ask to be in. The folks from Ventura Disc Golf are also a swell bunch of folks, I'm proud and privileged to know 'em. It also puts you about 20 minutes from downtown Ventura, which puts you close to Corralles, which has bar none the best burritos I've ever had.
De Laveaga (Santa Cruz, CA): Amazing variety of challenging holes, gorgeous NoCal scenery, and if it's not too hazy the view from 27 out over SCruz is truly breathtaking. My in-laws live close by, I get giddy whenever we plan a visit. I love the smell of the forest, the terrain, and the history. But aside from all that, it's one helluva challenge, and you'll get to use every shot in your bag.
Woodshed/Whippin' Post (Paw Paw, WV): My dreams about what kind of course(s) I would build if I had the land and resources aren't as spectacular as what Spencer Thurman built at Paw Paw. 65 acres of rolling pastures and woods, 2 courses packed with par 4's and 5's, gorgeous location and super swell people. Both courses totally redefined my concepts of what a disc golf course could be. The thing I like best about these courses is that with most courses, the story of any single hole is a short one: there's a really good drive or a not so good one; there's a great approach or a blown one; there's a long or a short putt. At Paw Paw, your immaculate awesome long drive ain't the end of the story, not even close, but the same goes for your totally shanked one. "There's still a lot of golf to play" doesn't just apply to the round, it applies to the hole itself.
Codorus State Park (Hanover, PA): If it only had one 18 hole course running through the woods and around Lake Marburg, and if that course only had 9 extended holes for those that require a serious humbling, it would be an awesome course. But there's two of 'em, see? And they're both excellent courses, great variety of shots, elevation changes, open rip-it holes and tight, technical ones. But if that's not enough, and you like throwing your mini Aviars around at lunch, then you can play a round on the 18-hole mini course too. There's camping across the street, boating, fishing, and all sortsa other distractions too.
Sylmar Upper Course (Sylmar, CA): I played this one in '06 at the Summertime Open (a two-day, four rounder that got up to 102 degrees if I remember correctly). Veterans Memorial Park is built on the grounds of the V.A. Hospital that was destroyed in an earthquake in 1971, and the permanent course (which is also really nice and a challenge besides) is built on the lower part of the park, but for the Summertime Open they put up a course on the upper grounds. If you've ever walked around an estate with interesting, rolling landscaping and thought, "man, this would be an incredible place for a course, but no one would let that happen here", that's the kind of course they put in for the tournament. If they're still doing it, and you're in the area around tourney time, it's gorgeous and definitely worth playing.
La Mirada (La Mirada, CA): I haven't been to La Mirada in several years, but I know they've taken out several holes from when it was a 27 hole course to make way for development. It's not as any of the other courses on my list, it's more of a city park with playgrounds, and pretty well manicured. But it's got great rolling terrain, some awesome big shots, and it's really pretty, and . One of the holes they tore out (breaks the heart, it does) hugged a left-to-right turning ridge of a slope that dropped down probably 30 feet or so to a grove of birch trees, the basket was on the slope a few hundred feet ahead. Oh, man, I just saw that Mike Williams' pro shop has closed. *sigh*
Seneca Creek (Gaithersburg, MD): Gorgeous park, now with 27 holes! This course is a classic, gorgeous forest holes, elevation holes, and those cedars... those cedars. Love this course. The holes along the creek are gorgeous, the ones through the trees will test you, and the two meter sticks leaning next to the cedars let you know that 1. the two-meter rule is always in effect here, and 2. people spend a lot of time digging into those branches. They're like disc velcro. It's an amazing course with a lot of history and it makes you earn every shot. Wish they allowed beer.
Rockburn Branch Park (Elkridge, MD): Beautiful 18 hole course less than an hour from DC and even closer to Bawlmer, hon. There's a lot of trees, some water, a bunch of different looks, shots, and challenges to put you to the test. But it's also really pretty, and wraps itself around and through some historic buildings and structures. It's like Brandywine that way, you can feel the history as you walk the course, but it's a much tighter, woodsier course. Stay on the fairways in the summer, or at least make sure to take a couple discs you won't mind saying goodbye to if they leave the fairway.
Waller Park (Santa Maria, CA): It's not the hilliest course, nor the most technical, but it is challenging, beautiful, and a lot of fun. I always try to get in a round there when I'm in the area. The front 9 draws you into the front of the park where the trees are well placed, but not super dense. The middle nine takes you deeper into the park for some technical work, and the last nine gets you out into the field for some longer, wider open shots. The Santa Maria Disc Golf Club is chock full of great folks, I always loved seeing them at SoCal events, and if you should win one of Lawrence Halili's gorgeous hand-made trophies, you'll be stoked.
Druid Hill Park (Baltimore, MD): This is a gem of a course smack in the middle of Baltimore, right next to the zoo, featuring 18 holes with long and short concrete pads, and 9 X-holes through the deeper parts of the woods. It's got a great mix of open, elevation, lightly and heavily wooded technical holes, and it's really fun to play.