Hero's is worth a look too. It gets next to no coverage in the UK which is a real shame considering the scale of the events. Hero's is run by the owners of K-1.
They have some reasonably big-name fighters, Genki Sudo, Don Frye, Heath Herring, Semmy Schilt, to name a few. Melvin Manhoef's a regular name on their fightcards. Quite a few lesser-known-outside-of-japan, Japanese fighters too - Hideo Tokoro & Kid Yamamoto.
They just did an event in the USA, Dynamite USA which smashed (i.e. doubled and then some) the UFC's attendance record which was just over 19,000 (compared to Dynamite USA's 43,000).
The only real problem is they don't have an english website so their events can be hard to track down.