Until now, my favourite games have all been the predictable "big ticket" items like GTA and COD. But I now own Trine, Toki Tori and Plants vs. Zombies. What fun they are and how shallow I've been in the past! What smaller, less obvious titles take your fancy?
PvZ is quite unique in a way so it's difficult to find similar games, but it's usually known as being in the tower defense genre. Have a look at Defense Grid: The Awakening
quite enjoyed Delve Deeper, a turn based game where your team of dwarf miners must try to get more money than the other teams (hot seat multiplayer only at the moment, although I've heard the sequal should have online multiplayer).
Angry Birds? Flight Control? Peggle? what are you looking for exactly? similar as in similar in gameplay (eg, tower defence) or similar as in similarly simple yet fun-to-play games?
These are the only games I play. Trine is just a platform game, and PVZ is just a tower defence game, and there are thousands of those. You should check out a website called Kongregate, because it's filled with free flash games that are similar. They are not as good looking as Trine, but there are thousands of platform and defence games that are all about great gameplay. p.s. Try Portal if you haven't already.
You should try Defence Grid - The Awakening also on Steam, another tower defence game that is very good. Lots of replay ability as well.
Some very good suggestions gents. Thanks. Now all we need is another Steam sale! Ah, but I already own Portal - which I've never played. It's now on the "to do" list.
I didn't think Defence Grid was all that great. It's ok, but it's a bit short, and I don't think it has good replayability. It's just a bunch of missions so once you know how to win them, you can just repeat it again the next time which isn't very interesting. I prefer something like Desktop Tower Defence where the play area is completely open so you can try different layouts each time.