I just voted on the poll, but I figured I would suggest a few more subjects for photo contests. Just a few ideas that come to mind are:

1) puddles
2) doors
3) trains
4) buildings
5) bridges
6) rain
7) waterfalls
8) fences
9) reflections
10) moon
11) holidays
12) candles
13) macro
14) aerial

add

15) seasons - pictures must depict spring (or winter etc)
16) portraits
17) babies
18) zoo (probably duplicates "large animals" but there are also small animals/reptiles/fish/birds at the zoo
19) birds
20) colors - e.g. any subject but the color RED for example, needs to predominate
21) bugs (in case we want to get more specific than "macro"
22) flowers (in case that's not what is intended by "plants"
23) night photography
24) heat
25) ice
26) snow