WordMonger
I'm extremely happy with my G1 so far. Gmail and Gtalk are especially good. The browser feels more robust than the iPhone's, but scrolling and zooming is a lot choppier. I've made more use of onscreen keyboard out of necessity, like while standing up on a busy train or holding coffee, and I think it's better than the iPhone's.

One thing I'm really missing right now is CheckWord, so replacing that with a tool of my own is a high priority. I played around with the Android SDK this weekend, mostly just playing around with layouts of interfaces.

Here's a mockup of the basic word search. Since that was taken I added "Spinner" (like a dropdown list, but it fills up most of the screen to make it easier to read and touch your choice) widgets for selecting the search type (Anagram, Build, Pattern, or Steal) and lexicon (for the sake of space and discretion, I'm thinking of calling them "US '06" and "UK '07"). The latter might not get switched often enough by most people to warrant being on the main screen, and I think it should at the very least it should disappear while holding the screen upright in portrait mode.

I scribbled a picture of a custom onscreen keyboard while waiting for a meeting to start, and it was very easy to make it actually work.

Ideas I've had for the word search:
optionally coloring/marking words for #ness or newness
coloring blank letters
somehow displaying anamonics and definitions
some "hint" mode where instead of giving the words in the result, it just says how many results there are, or which letters the blanks are, how long the shortest steal is, etc
words appear in fixed-width type in columns and scroll left to right

And for other functionality:
word judge (full-screen with instructions and lexicon setting displayed)
"views" for words, like Bob's Bible-style anagrams and hooks, or flipping through dictionary pages
Jumbletime/Aerolith grid quiz mode (might be tolerable with a physical qwerty keyboard like my phone has)
Zyzzyva/Letterbox-style study mode