Sudoku is easy to understand: All you have to do is fill in a grid with numbers.

Within those constrictions, it turns out, there's a lot of room for variety, and a sudoku puzzle can be easy enough for a child or hard enough to torment a university logician.

Lately there's been a boom in computer programs and handheld devices that play sudoku. Electronic sudoku has a few advantages over the paper version: It's easy to erase mistakes, and you can have the computer warn you when you've goofed up.

• Click here to visit FOXNews.com's Video Gaming Center.

It should be an easy thing to translate into a video game, but I've been surprised by how many crummy sudoku programs I've seen over the last two years.

Ubisoft's "Go! Sudoku," which came out last year for the PSP, is the best of the bunch, but it has gotten some competition lately.

— "Carol Vorderman's Sudoku" (Eidos, for the PlayStation Portable, PlayStation 2, $19.99): Carol Vorderman's site describes her as "one of Britain's best known and loved TV personalities"; a handful of her sudoku books have been republished in the U.S.

In her video game she presents an assortment of sudoku-solving tutorials, and players will find her preference for low-cut dresses either fetching or annoying.

The real attraction of "Vorderman," however, is its clean, easy-to-use interface.

Many similar games feel the need to dress up their simple puzzles with intrusive, Asian-flavored graphics, but "Vorderman" sticks with elegant black-and-white grids.

With over 1 million puzzles, four difficulty levels and a variety of ways to solve (including timed, career and multiplayer challenges), this is a robust package that will please any sudoku addict.

Three stars out of four.

— "Brain Buster Puzzle Pak" (Agetec, for the Nintendo DS, $19.99): "Brain Buster" also benefits from clean, readable screens, although its overall design is a little clunkier than the Vorderman game's.

My major complaint with it is that it forces you to tackle puzzles in order from easiest to hardest, meaning that sudoku vets who want a stiff challenge will have to slog through dozens of no-brainers first.

What makes "Brain Buster" a bargain, however, is that it features four more puzzle types from Nikoli, the publisher that popularized sudoku in Japan.

Only kakuro, a sort of cross-number addition puzzle, will be familiar to most American solvers.

The others — nurikabe, slitherlink and light up — work the same brain cells that you'd use in a game of "Minesweeper"; the numbers in the grid give you clues to the locations of walls, black squares or light bulbs.

Puzzle fans who have burned out on sudoku should give "Brain Buster" a try.

Three stars.

— "Toon-Doku" (Majesco, for the DS, $19.99): "Toon-Doku" has a cute, kid-friendly gimmick: instead of filling in numbers, you're lining up tiny cartoons.

Unfortunately, the pictures are so small that it's sometimes difficult to tell them apart; a lemon may look an awful lot like a pie.

"Toon-Doku" also clutters up the screen with hectic background images that too often overlap with the pictures you're trying to arrange. Fortunately, you can always switch back to more readable numerals.

The puzzles are pretty good, the game mechanics are sensible and there are lots of different ways to play. And as a bonus, the more puzzles you solve, the more cartoons you get.

Two stars.

— "Sudokuro" (Crave, for the DS, $19.99): The low-budget, low-quality publisher Crave has previously unleashed such abominations as "The Bible Game," "NRA Gun Club" and "Purr Pals."

"Sudokuro," which combines sudoku and kakuro in one unplayable package, lives down to Crave's dreadful reputation.

Inexplicably, "Sudokuro" puts its puzzle grids in the top (non-touch-sensitive) screen of the DS, so you can't even use the stylus to move around the diagram.

There's no way to put multiple numbers in a space, an essential solving technique for trickier problems. And the quality and skill ratings of the puzzles are haphazard; supposedly "easy" kakuro puzzles are so poorly designed they're next to impossible.

No stars.