This may be more work than you want, but you might try something like this:
Token Pool: Every character has a number of tokens = character level
Spend Rate: 1/2 character level. This is the maximum number of tokens that can be spent on any one ability. Spending tokens is typically a swift action, but can be spent as an immediate action (ignore flat-footed restrictions) if the player so desires.
Token Abilities: Tokens can be spent for the following purposes:
*Dodge - Each token spent adds +2 to the character's AC for one round.
*DR - Each token spent grants the character DR 2/- for one round.
*Saves - Each token spent grants the character +2 to their next save.
*Skillful - Each token spent grants the character +2 to their next skill check.
*Tumble - Spend a token to avoid an AoO caused by movement. Every AoO opportunity requires a separate token (thus if 3 giants can attack you, spending one token only avoids one AoO - the other two still attack)
*Resist - Each token spent grants you 2 points of energy resistance to one element for one round
There are other abilities that you could come up with. I'd only recommend using tokens for significant npc's - ignore the mooks, otherwise the GM will be swamped keeping track of it all.
As for refresh, you can simply declare the token pools refreshed at the end of the encounter, or allow characters to recover one or more tokens by expending a full round action. To prevent some abuses (primarily with skills), you can limit tokens to being used only in combat, say after initiative is rolled, but before anyone acts.
If you want to limit the abilities characters can use tokens for, grant them bonus feats that are used only for selecting these abilities - maybe one at first level, and one at every fourth level (1, 4, 8, 12, 16, 20). This is probably a good idea if you have a lot of different abilties available for token use.