!SolarWinds is probably the most popular free TFTP server out there. The only downfalls/issues is the banner and the size at 8.71 MB. I came across a lightweight one recently that works extremely well called Tftpd32. It even supports files larger than 4 GB. It's size is considerably smaller at 479 KB.

You can find it at: http://tftpd32.jounin.net/

It also works as a TFTP client and provides DHCP, SNTP, and Syslog capabilities. Tftpd32 also supports being ran as a Windows service.

– Main.FredPettis - 11 Mar 2009