Level 1: 0-1499 xp (+1500)
Level 2: 1500-3999 (+2500)
Level 3: 4000-7999 (+4000)
Level 4: 8000-14999 (+7000)
Level 5: 15000-24999 (+10000)
One Chart: This is my personal preference. I like to try for my character classes to be balanced choices from the start, not artificially balanced by factors that come into play weeks or years after you've made your pick. Balance is of course secondary to making sure the party has a good selection of abilities to call on, but I'm not blind to the ways of players who may be checking out where other players are going with their character choices.
The classic example in D&D-like games is the 1250 xp needed for a thief to reach 2nd level versus the 2500 for a magic-user. Even more odd is the mere 1500 xp for the cleric, who enjoys the second best fighting stats and a unique and necessary skill set. The 1500 figure made more sense in OD&D when the cleric was a hybrid fighting / magic class who had to wait until 2nd level for spells. In fact, I get the feeling, reading old rule sets and retroclones, that experience rules - the most important aspect of strategic game pacing - suffer from a lot of received ideas, and not a lot of thought about what actually works. ("Oh my god! They had an all-class experience chart in The Edition That Shall Not Be Televised! We must purge it with fire!")
If a rogue is a weaker choice than a wizard I'd rather make the rogue stronger than make the wizard lag behind in levels. This is what I've tried to do in my house-rules, by making the rogue better at attacking, eventually good at defending (through level-based AC dodge bonuses) and able to score extra damage through sniping as well as backstabbing. I've also restricted the wizard a good deal with the only one of each spell rule.
1500 xp to 2nd Level: In my campaign, which meets weekly at best and until recently had quite short sessions, this was a decent pacing. A good session would net each character 200-300 xp and there were enough brushes with death and dismemberment to really drive home the exquisite joys of old school 1st level. 2000 would not be unreasonable, either, given the large sums I'm granting for monsters.
Progression: Each level takes about 1.6 times as many XP to reach as the previous. Not sure how this will go, naturally, but it seems in keeping with tried and true principles. The implication, in case I ever get around to cooking up random encounter and treasure tables, is that the XP of monsters and wealth of treasures should follow a similar progression.
The purpose of a sharper progression is to reduce grinding and reward taking on risky challenges. For example, if the XP to advance doubles every level (as in Labyrinth Lord, once past the 2nd level), and the XP from monsters and treasures available also doubles every level, then a 5th level party killing orcs rather than 5th level fare will only net 1/32 of the advancement. But this system kind of breaks down when it comes to treasure. Having 32 times the treasure at level 5 as at level 1 is great but leaves very little room to go upwards in any meaningful way. Still, trying to reduce experience from fighting overly low-level monsters through specific XP reduction rules turns out to be unwieldy in practice, as you get into calculations of average party level and the like. Doing it naturally, through a level table where you need more and more to advance, seems better.
Well, those are the basics. Three categories to follow: XP from monsters; XP from treasure; and XP from ... other activities. Thoughts welcome, as always.