Oh, God, Cchiu, now I have to remember what I've done - let's see - mostly oriental greens, baby bok choy, mizuna, garlic chives, stuff like that. I'm not a big bitter melon fan. We have Asian supermarkets here that carry all the seeds and even some seedlings in the spring, so I'm pretty lucky on that front.
Tomatoes - I order seeds from The Cook's Garden
www.cooksgarden.com They have heirlooms, and lots of European varieties, too. I also buy seedlings from this totally funky place here - The New Jersey Botanic Gardens; they're absolutely awesome in the varieties of tomatoes, peppers, herbs, and annuals/perennials - I have done major damage to my pocketbook there!!! I also get a catalog called "Totally Tomatoes", which has an amazing selection from all over the world - even Russia! I just checked their website, but they don't have one anymore.
Peppers - I usually plant seedlings, and have planted them all!!! The big thing I learned is you have to watch your length of time to harvest - lots of peppers need a long, hot growing season, more than we have in NJ, so I wasn't too successful with some of the Mexican varieties. But I did get a good crop of ancho chiles, pasilla, and guajillo, and of course, jalepeno. If you like jalepenos on the hot side, watch what you buy. Texas A&M has messed with the jalepeno to get a 'milder' one; tastes like a green bell pepper - what a sacrilege!!! Oh, and one year I grew a Datil pepper, a little tiny thing about the size of a pea, and round. Being the macho chili queen that I am, when my hubbie challenged me to eat one while in the garden, of course I did; the distance between the garden and the house never seemed so long!!!! I have NEVER eaten anything so hot in my life! Also grew a Japanese chili, which was quite nice - can't remember the name, but it meant 'hawk's claw' cause that's what it looks like. There's a nursery here in Jersey that ships seedlings; I'll try to find the address for you, they have an amazing variety, too!
And tomatillos are fun, too; they're a pretty plant, but sort of large and somewhat viney.
Hope this helped.