dunno where you'll be putting the compost though.....
Seriously though, nearly everything can be done in modules... you might have to get specific as to variety though... I doubt Cylindra beetroots would like them much but Boltardy works well, as do the ball-rooted monogerm varieties. Not peas, beans or sweetcorn as they need more space, though you'd get away with the 15-drop tray ones I guess... onions work well, all sorts really, giants and big mains on thier own in a 40-drop in a propagator in January, cluster mains 4 or 45 seeds in a 40-drop, pickling and spring say 10 seeds per module in a 40-drop.
All the brassicas including swede will work and you avoid some of the shock of transplanting.
Salads, especially lettuce.
Herbs: parsley, oregano, both chives, thyme and basil all work well, along with coriander and fennel.
Contrary to popular opinion you can start carrots and parsnips off in modules. Get a 24-drop and populate it with toilet roll tubes for carrots and kitchen-roll tubes for parsnips... tie them up with something to stop them flopping around.. fill with compost and sow 2-3 (maincrop carrots and parsnips) to 7-10 (baby carrots) seeds in the top of each... plant out once they've got going properly... no thinning means less carrot root fly damage hopefully.....same system should work on other long-roots like mooli, hamburg parsley etc
All the standard GH tender veg will work, tomatos, peppers, chillis, aubergine, okra etc, though the cucurbits will need the 15-drop ones. Same goes for the outdoor cucurbits, gherkins, courgettes, squashes and pumpkins.....
I do nearly everything except tubers in modules to start... and there are sevreal good reasons to:
1 it saves on seed wastage, helpful if its an expensive seed that will last but there's more in the packet than you need
2: They take up less space meaning you can keep them somewhere better protected frrom the elements and pests,
3: It also allows you to get your sowing done when you want rather than needing a nice day.... which means earlier starts for several things that like long growing seasons like celeriac, parsnips and leeks
chrisc
4: quite a lot of them can be planted out through weed-supressants as small plants, saves on the weeding a lot....
chrisc