A couple of years ago I wasted a lot of time playing When Penguins Attack. It’s easy to play on a laptop without a mouse or separate keyboard. Anyone have suggestions for another game I can waste time with?
FarmVille.
Tower defense games, eh? My favorite!
I think the number one entry in this genre is the “Gemcraft” series; while you are limited to the preselected pathway (for the most part) you have good control over where you wish to put your towers otherwise, as well as the ability to place traps on the path itself. The outstanding feature of this game is that you can combine gems to create different effects… for example, you can combine a red (multi-target) gem with a blue (slowing) gem to slow down and damage mutiple targets at once. Three games available, Gemcraft: Chapter Zero being my favorite.
Another top-level tower defense game is the “Protector” series… at least, those which are tower-defense based. There are others that are less about towers and more about, well, other stuff. While the paths are still predetermined, you’ve got lots of good places to put your ‘towers’ (actually individual combat units) along those paths. The selling point of this game is that the units gain experience for kills, and you get a ‘tree’ to let you choose upgrade paths, which differ depending on the unit type. For example, you might make your melee units hit harder or faster, or you might give your ranged units faster reloading or more chance to do critical damage. The best of this series is Protector IV.V but you may wish to start with the earlier games in the series, such as the original Protector.
Yet another pre-determined pathway game is the ever popular “Bloons” series. Instead of monsters, you’re using variously-armed monkeys to pop balloons (why the balloons are considered dangerous is never adequately explained.) Some upgrading available, based solely on money instead of experience, lets you decide what path each tower type might follow. Lots of different maps to play, with various options, and they add new maps and new variations on a fairly regular basis. Currently on the fifth iteration: Bloons Tower Defense 5, don’t bother with the earlier versions unless you really want to.
One of the best entries in the make-your-own-pathway games is Desktop Tower Defense, which offers a pretty good variety of options in terms of maps and such. Can be very challenging at higher levels!
Bubble Tanks Tower Defense is another option where you make your own pathway. Kinda cutesy, but still challenging. Main selling point is that you can combine towers into mega-towers and mega-mega-towers for super ultimate power!
And then there are the games where you’re limited in where you place your towers, AND the paths are pre-determined. Not my favorite, but there are some good games in this category. Demons vs. Fairyland, Takeover, and Incursion are all worth a play, I think.
That should hold you for a while, I hope! Let me know when you get bored with these, I’ve got more… 
The only tower defense game I’ve ever liked is Plants vs. Zombies. It costs $20, but I have a bunch of codes leftover from the Halloween giveaway. (And, no, I don’t mean the coupon. I actually used the coupons to get codes, so I could give the game away to anyone who wants it, even past the coupon registration date.)
I guess I have less time to waste than I thought!
First, curse you Johnny L.A. for those Penguins! 
Second, It took me 3 days, but in “When Penguins attack 4” (Yeah, I did solved all) why is that the last level #10 remains locked? (this is after getting all 3 medals for all the previous levels)