Petunias in peat pellets. About one of the only seedlings I start in peat pellets. They seem to work really well for the teeny-tiny seeds. I'm not huge on peat pellets, since I find they can dry out awfully quickly after the seeds germinate. 
 

Onion seedlings. I am not a huge fan of these plastic trays, cells and domes either, however I bought them a few years ago and am going to use them until they fall to pieces on me. It can be hard to try and use environmentally friendly cells for starting seeds. I was not really thinking about that when I bought the plastic trays several years ago. Things like egg carton trays hold an awfully lot of moisture and are not really the sturdiest for moving around. The plastic containers are made of petroleum, which we try and avoid or use as little as we possibly can in our home and everyday lives including gardening.  It's great to use something environmentally friendly, it is just too bad that it defeats the purpose if the durability is questionable. I like re-using things like tetra packs from juice, old yogurt containers, little tins and glass jars. The peat pellets I bought are supposed to be from sustainable peat moss from New Brunswick, with the packaging boasting how there is no shortage of peat in N.B. This is an area that I really need to research much further.  

Ground cherry seedlings. I like to get a few of these started early since they will give off the little ground cherries starting in June.