In these tough economic times, everyone's looking for a bargain. Luckily, we just found Galaxy Wars on Kongregate, and it's one of the best (free) shoot-em-ups available on the PC. Galaxy Wars has ship upgrades, several different ways to take out enemies, and a distinct Geometry Wars vibe:

The game feels very modern for a shmup -- you can purchase upgrades on the fly, and, as the levels go by, the number of enemy ships on-screen at one time is staggering. There's even a crappy graphics option for people with crappy PCs. Dramamine not included.