Just about EVERYTHING along Main Street (Old Town) is good from breakfast to dinner. Parking is sometimes a problem - watch the signs VERY carefully - the parking restrictions vary from one street to the next & the enforcement is frequently monitored. Enjoy a stroll out the pier and stop in at Ruby's for a shake or whatever.
Our personal faves are Walt's Warf (sea food), Old Town Cafe, the bbq place (squeeze right in!), the Hawaiian place (Kinda La'Haina is the name or a close facimile) for breakfast and a great place for people watching along the street-facing tables, O'Malley's for breakfast or lunch (haven't been for dinner) . Just about all the other places there are also favorites of many Hounds - I don't think you can go wrong on Main Street.
There's also a wine tasting place, and a old time theater that screens older films. Real pipe organ inside, though I don't know if it's used now. Fun places to wander through: the old hardware store, Brita's Garden, the shell souvenier shop, among several others. Only thing missing is a cozy spot for a bookstore but there is a Christian Science Reading Room that always seems to be open. Occasionally the red trolley is open for tours, and there's a public library just beyond that.
Bakeries and dessert places, and two pizza places practically next door (or maybe they are) to each other. Several new dinner places have opened recently but we haven't tried them yet. Many of the places are dog-friendly (dogs outside or along the patio) with water bowls waiting.
There are also several other places within a good brisk walk or short drive heading north. Enjoy!
As the OP mentioned, anywhere on Main Street. Old Town is great for breakfast and lunches but they close right after. I forgot the name of the small Mexican place next door but that place is great also. For high end dining try Spaghettini up on Seal Beach Blvd.
Main Street Cafe
12939 Main St, Garden Grove, CA 92840
2nd Beachwood BBQ, especially for the beer selection they have. One of the best microbrew selections anywhere. Patty's Place is a great neighborhood steakhouse and a great place to have cocktails and/or eat at the bar. I have eaten there a hundred times and never had a bad meal. 320 main has good cocktails too. Angelo's deli makes great sub sandwiches.
we've lived in SB for three years, and the only two places we could really recommend are Koi sushi in PCH (outstanding; sit in Daigo;s section (sp?)) and La Crema for breakfast, pastries and coffee. We've heard consistently good reviews for Walts but have not gone.
322 Main St, Seal Beach, CA 90740
Everyone seems to forget Cafe Lafayette - probably because it's sort of hidden, down by the theater - but it is a favorite of the locals for upscale breakfast, lunch and dinner - only bested by Walt's for seafood.
520 S La Fayette Park Pl Ste 107, Los Angeles, CA 90057